Bibliography in Assisted Reproductive Technology (ART)

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In an ever-evolving field marked by rapid scientific progress and increasing clinical complexity, it is essential to remain updated on key innovations, best practices, and the most relevant publications.

Compiled and reviewed by the clinical team at the Centre de FIV de la Muette—one of Paris’ most established and active ART centers—this summary offers a concise yet rigorous overview of recent advances in the field. Drawing from high-impact international journals, the work highlights emerging techniques, evolving protocols, and critical findings in ART.

With this bibliographical review, we aim to offer an original tool to aid in scientific monitoring, positioned between the conventional abstract and the often lengthy and time-consuming full reading of the original article. This hybrid format ensures substantial time savings by enabling the rapid and targeted identification of publications that, based on their content, warrant an in-depth reading.

Regular updates will follow to keep pace with the dynamic landscape of ART.

Sperm Parameters and Assisted Reproductive Technology Outcomes

Dr Anne Dupont

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Dr Cécile François

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Dr François durand

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Overview

While Assisted Reproductive Technology (ART) offers solutions for various forms of infertility, predicting the success of these treatments remains complex. Male factors, specifically characteristics of sperm evaluated through semen analysis (sperm parameters), are considered potentially influential factors. This synthesis explores the predictive value of various sperm parameters for ART outcomes, drawing upon findings from the provided literature, which includes studies comparing IVF and ICSI, systematic reviews, and analyses of specific sperm characteristics like morphology and DNA fragmentation.

Sperm parameters assessed in semen analysis typically include semen volume, sperm concentration, total sperm number, progressive motility, total motility, and normal sperm morphology. The World Health Organization (WHO) has published several editions of its laboratory manual for semen examination, introducing methodological differences and changing reference ranges across editions. For instance, the 5th edition defined oligozoospermia as sperm concentration <15 million/ml and/or total sperm count <39 million, asthenozoospermia as progressive motility <32% and/or total motility <40%, and teratozoospermia (defined by normal morphology) as sperm morphology <4%. These definitions differ significantly from previous editions, such as the 3rd edition where teratozoospermia was defined by morphology <30% and the 4th edition by <14%. Studies have noted differences in detected semen parameters when using the WHO 5th edition manual compared to previous editions, with higher semen volume and total sperm number, but lower sperm concentration, progressive motility, and sperm morphology observed with the 5th edition.

Beyond basic parameters, sperm DNA fragmentation (sDNAfrag), often measured as the DNA Fragmentation Index (DFI), is another characteristic that has been investigated for its potential predictive value in ART. Different methods like the TUNEL assay or DBD-FISH technique are used to assess sDNAfrag. There are conflicting reports and a lack of consensus on appropriate cut-offs for DFI.

The sources present varying degrees of association between different sperm parameters and ART success metrics, such as fertilization rate (FR), total fertilization failure (TFF), clinical pregnancy rate (CPR), live birth rate (LBR), and ongoing pregnancy rate.

Some studies suggest that certain parameters are associated with improved outcomes. Progressive sperm motility and sperm morphology, according to the WHO 5th edition, were found to be associated with the overall fertilization rate per inseminated oocyte. Progressive motility and capacitation significantly predicted the total pregnancy rate. Notably, sperm morphology shows the strongest relationship in ICSI cycles, influencing both fertilization rate and final ART outcomes like pregnancy rate. A specific cut-off of 5.5% for sperm morphology was identified as a threshold to predict clinical pregnancy with high accuracy.

However, the predictive value of other parameters, like sperm DNA fragmentation, is less clear. Literature reports show contradictory findings regarding high levels of sDNAfrag. Some evidence suggests an association between high sDNAfrag levels and lower FR and CPR. Conversely, other reports found high sDNAfrag levels were not associated with FR, embryo quality rate, total number of blastocysts, or CPR. DFI was also not associated with birth characteristics such as birth weight and gestational age. The lack of consensus on DFI cut-offs further complicates the interpretation of its predictive role.

Furthermore, the predictive power of sperm parameters might depend on the specific ART technique used (IVF vs. ICSI) and the underlying cause of infertility. While ICSI was initially developed for severe male infertility, its use has expanded to other indications, including non-male factor infertility. Some studies focusing on non-male factor infertility indicate that ICSI does not improve LBR or other outcomes compared to conventional IVF in this population.

A secondary analysis of a large randomized controlled trial focusing on couples with infertility and normal total sperm count and motility specifically investigated the role of sperm morphology as a biomarker. This analysis suggested that, in this particular population, sperm morphology had limited value in identifying couples who would benefit more from ICSI over conventional IVF for outcomes such as live birth, ongoing pregnancy, clinical pregnancy, or total fertilization failure. These findings align with evidence from intrauterine insemination (IUI) studies regarding the limited predictive value of sperm morphology for clinical pregnancy.

TGA can occur as an isolated anomaly or in association with other cardiac and extracardiac malformations. When associated with other cardiac anomalies visible on the four-chamber view (e.g., ventricular septal defect, abnormal cardiac axis, chamber size discrepancy), prenatal detection may be easier compared to simple TGA with a normal four-chamber view. Chromosomal and extracardiac anomalies are relatively rare in isolated TGA, but their presence warrants consideration. TGA has been linked to maternal pre-gestational diabetes, exposure to pesticides, and first-trimester retinoic acid use.

Comparing findings across studies is challenging due to evolving methodologies and reference ranges in WHO semen analysis manuals. The differing criteria used over time can impact the reported prevalence of semen alterations (like oligo-, astheno-, and teratozoospermia) and measured parameter values.

Conflicting results, particularly regarding sperm DNA fragmentation, highlight the need for standardized assessment methods and consensus on clinically relevant thresholds. Limitations in studies, such as being potentially underpowered for specific outcomes or subgroups, or not evaluating a full range of relevant sperm tests (like DFI), can also impact the generalizability and certainty of findings. Some studies included in systematic reviews on ICSI vs. IVF in non-male factor infertility had high heterogeneity in results for certain outcomes like fertilization rate.

Conclusion

Based on the provided sources, sperm parameters, particularly morphology and progressive motility, show some association with ART outcomes like fertilization and pregnancy rates, especially in ICSI cycles. A specific morphology threshold (5.5%) has been suggested for predicting clinical pregnancy. However, the predictive value of other parameters, such as DNA fragmentation, is inconsistent across studies. Furthermore, the utility of sperm morphology as a predictive biomarker appears limited in specific populations, such as couples with normal total sperm count and motility, for determining the benefit of ICSI over conventional IVF. The interpretation of sperm parameter values is also affected by changes in international guidelines over time. While sperm parameters provide valuable information in the context of male infertility, their precise role in predicting ART success and guiding the choice between IVF and ICSI, especially outside of severe male factor cases, remains an area with conflicting evidence and requires further clarification through standardized research.

Bibliographie

Methodology and Scope

The study included a large cohort of ART cycles. Specifically, the analysis considered 5819 In Vitro Fertilization (IVF) cycles (26.4%) and 16,194 Intracytoplasmic Sperm Injection (ICSI) cycles (73.6%).

Semen analyses were performed using different editions of the World Health Organization (WHO) laboratory manual for semen examination. The study utilized data collected using the 3rd, 4th, and 5th editions of the WHO manual. It is noted that the 3rd (1992) and 4th (1999) editions showed only minor changes in methodologies and reference ranges, so results obtained using these two editions were considered together. The 5th edition (2010) introduced more significant methodological differences and changed reference ranges compared to previous editions.

Specific semen parameters defined by the WHO manuals are mentioned:

  • Oligozoospermia: defined as sperm concentration <20 million/ml and/or total sperm count <40 million (3rd/4th editions), vs. <15 million/ml and/or total sperm count <39 million (5th edition).
  • Asthenozoospermia: defined as progressive motility <25% and/or total motility <50% (3rd/4th editions), vs. progressive motility <32% and/or total motility <40% (5th edition).
  • Teratozoospermia (low normal morphology): defined by sperm morphology <30% (3rd edition) or <14% (4th edition), vs. <4% (5th edition).

A capacitation test was routinely performed for all patients.

Findings on Parameter Assessment Across WHO Editions

The source highlights that when using the WHO 5th edition manual, higher semen volume (p < 0.001) and total sperm number (p < 0.001) were detected compared to previous editions. Conversely, using the 5th edition resulted in lower sperm concentration (p = 0.004), progressive motility (p < 0.001), and sperm morphology (p < 0.001) compared to earlier editions. These differences underscore the impact of evolving laboratory standards on reported sperm parameter values.

Predictive Value of Sperm Parameters for ICSI Outcomes

The provided excerpt presents an analysis of factors predicting outcomes specifically in ICSI cycles. Several sperm parameters, along with male age, body mass index (BMI), and smoking habit, were included in this analysis.

According to the table presented, within the context of ICSI cycles, progressive sperm motility (%) was found to be a statistically significant predictor (p < 0.001). The beta coefficient suggests a positive association with the outcome being measured in this specific analysis (though the outcome itself is not fully specified in this excerpt, the column headers “Beta coefficient 95% confidence interval p-value” and the context of predicting ART success point to a predictive model).

Other parameters analyzed in the ICSI model included semen volume, sperm concentration, total sperm number, and normal sperm morphology. For normal sperm morphology (%), the p-value was 0.158, indicating it was not statistically significant as a predictor in this particular analysis presented in excerpt. Semen volume, sperm concentration, total sperm number, male age, male BMI, and male smoking habit were also not statistically significant predictors in this specific model (p-values > 0.05).

Study Funding and Conflicts

The study authors declared that this specific study did not receive funds. Furthermore, the authors stated that they have no conflict of interest. Author contributions to various aspects of the study, including design, data acquisition, analysis, and manuscript drafting, are also listed.

Conclusion (Based on Excerpts-)

Based on the analyzed excerpts from this source-, the study included a large number of ART cycles, predominantly ICSI. A significant finding related to sperm parameter assessment is that using the WHO 5th edition manual leads to reporting different values for key parameters (higher volume/total count, lower concentration/motility/morphology) compared to earlier editions. In the specific analysis presented for ICSI cycles, progressive sperm motility was identified as a statistically significant predictor, while other parameters like normal sperm morphology did not reach statistical significance in this particular model. The study was unfunded and the authors declared no conflicts of interest.

This document presents a systematic review and meta-analysis conducted to clarify the efficacy of Intracytoplasmic Sperm Injection (ICSI) in couples with non-male factor infertility. Recent randomized controlled trials (RCTs) have become accessible, providing more reliable results regarding ICSI efficacy. Therefore, this new systematic review and meta-analysis of RCTs was deemed necessary to address limitations in existing reviews and provide robust evidence.

The study followed the guidelines of the Cochrane Handbook for systematic reviews of interventions and was registered in PROSPERO (CRD42023427004). It also adhered to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) checklist.

The search strategy involved a comprehensive search of Medline (via PubMed), Embase, and Cochrane Central Register of Controlled Trials (CENTRAL) from their inception up to March 2023, including only English publications. Additional relevant data were sought by manually checking references of conference proceedings, identified studies, or clinical trial registries. There were no limitations regarding publication status or sample size.

Study selection was performed independently by two authors, resolving disagreements through discussion with a third author. Data extraction was also conducted independently by two authors and cross-checked, with discrepancies discussed with a third author. The extracted information included details such as the first author, country, publication year, study period, study design, unit of randomization, etiology of infertility, exclusion criteria, methods for evaluating sperm samples, sperm preparation techniques, insemination concentrations for IVF, female age, number of patients/cycles, number of retrieved oocytes, controlled ovarian stimulation protocol, and primary outcomes.

For data synthesis, the Review Manager program version 5.4 was used for meta-analysis. Due to the clinical heterogeneity among the included studies (variations in protocols and participant characteristics), a random-effects model was utilized to pool overall estimates. The risk ratio (RR) with a 95% confidence interval (CI) was calculated for dichotomous outcomes. The I-squared (I²) statistic was used to assess data heterogeneity, with substantial heterogeneity indicated by an I² > 50%.

Initially, database searches yielded 1838 records, with an additional 10 from other sources. After removing duplicates, 1796 records were screened based on titles and abstracts, leading to the exclusion of 1725 records. Full texts of the remaining 71 studies were assessed for eligibility, resulting in the exclusion of 53 studies for various reasons, including male-factor infertility (28 studies), non-ICSI (14 studies), non-IVF (4 studies), missing primary outcomes (5 studies), or inability to obtain original data (2 studies). Ultimately, 18 randomized studies were included in the quantitative synthesis (meta-analysis). These included studies from references such as Aboulghar et al. (1995, 1996, 1999), Yang et al. (1996), Ruiz et al. (1997), Bukulmez et al. (2000), Bhattacharya et al. (2001), Poehl et al. (2001), Khamis et al. (2001), Jaroudi et al. (2003), Hwang et al. (2005), Foong et al. (2006), and Isikoglu et al. (2019), among others.

Detailed characteristics of the included studies are provided in Table 1. A total of 18 RCTs involving 3249 cycles and 30,994 sibling oocytes were included. The average female age in these studies ranged from 29 to 41 years. Eleven studies used sibling oocytes as the unit of randomization, while the remaining studies randomized patients to ICSI or IVF groups. The etiology of non-male factor infertility varied, including tubal factor, unexplained infertility, polycystic ovary syndrome, low ovarian response, and multiple causes. Twelve studies followed WHO’s sperm evaluation criteria, while six others combined WHO criteria with Kruger’s strict criteria. Different sperm preparation techniques were used, including discontinuous gradient and swim-up.

Regarding the risk of bias, nine trials were rated as having a low risk for random sequence generation, and four for allocation concealment. Four studies explicitly reported blinding of outcome assessors. However, blinding operators was considered potentially impossible in studies randomizing sibling oocytes. Twelve studies were judged to be at high risk of performance bias.

The study investigated the Fertilization Rate (FR) per oocyte retrieved across all included studies. The results showed no significant difference in FR per oocyte retrieved between ICSI and IVF (RR = 1.05, 95% CI: 0.98–1.13, I² = 92%, 30,994 oocytes). The high I² value indicates substantial heterogeneity in the data. However, the authors note that ICSI showed a much higher FR when considering FR per oocyte inseminated/injected. This difference in FR might be explained by the fact that in ICSI, only mature (metaphase II) oocytes are injected, whereas in conventional IVF, some metaphase I oocytes can mature in vitro and fertilize, increasing the overall FR in the IVF group when calculated per oocyte retrieved.

Another primary outcome examined was Total Fertilization Failure (TFF). TFF is described as a significant emotional and financial blow to patients and a main reason for the wide use of ICSI in non-male factor infertility. While many studies have suggested ICSI could reduce the risk of TFF, this meta-analysis observed only a trend of TFF reduction with ICSI. The authors calculated that approximately 50 additional cycles of ICSI would be needed to avoid one occurrence of TFF after IVF, arguing against the routine use of ICSI solely for TFF reduction.

In terms of Live Birth Rate (LBR), the meta-analysis reported an anticipated absolute effect where 308 per 1000 cycles resulted in live birth with IVF, compared to 342 per 1000 (95% CI: 290–400) with ICSI. The difference was 34 more live births per 1000 cycles with ICSI, but the confidence interval (-18 to 92) indicates this difference was not statistically significant. The relative effect (RR 1.11, 95% CI: 0.94–1.30) also did not show a significant difference. This finding was based on data from 1190 cycles across 3 RCTs. The certainty of evidence for live birth was assessed as moderate according to the GRADE approach.

The authors highlight several unique strengths of their research. It is described as the first meta-analysis focusing strictly on randomized trials comparing ICSI and IVF for non-male factor infertility. Compared to previous studies often focusing on FR, this analysis placed a greater focus on clinical outcomes, aiming for comprehensiveness. The study was registered in PROSPERO and conducted strictly according to the Cochrane Handbook. Subgroup analyses were performed to explore the influence of different factors on outcomes. Notably, this review was the first to investigate the impact of the randomization unit (sibling oocytes vs. patients) on outcomes, finding significant differences in key outcomes depending on the unit of randomization.

However, the study also acknowledges main limitations. It did not analyze or summarize congenital disabilities and neonatal growth. Only one included trial reported neonate-related outcomes, showing no significant difference between the groups. There was also a lack of relevant data on thawing cycles. High heterogeneity was observed in the FR analysis, potentially related to differences in sample sizes, study protocols, and participant characteristics. Finally, the analysis could not assess the impact of various etiologies on outcomes due to limited available data.

In conclusion, based on this systematic review and meta-analysis of RCTs, ICSI showed no significant difference in fertilization rate per oocyte retrieved, live birth rate, clinical pregnancy, or ongoing pregnancy compared to conventional IVF in couples with non-male factor infertility. While there was a trend towards TFF reduction with ICSI, the number needed to treat was high. The study suggests that for couples with non-male factor infertility, ICSI does not appear to offer a significant advantage in terms of key fertility outcomes, and the routine use of ICSI solely to avoid TFF is questionable based on the observed ratio.

A major milestone was reached in 1992 with the first reported human birth via intracytoplasmic sperm injection (ICSI), a technique involving the microscopic injection of a single spermatozoon into a mature oocyte. Successful ICSI has become a reliable therapy for infertile couples. However, the widespread adoption of ICSI has also introduced various challenges. The review explores the history of ICSI, including early attempts, the first successful applications, critical reports reflecting initial skepticism, and the chronological progress leading to its wide application. The main findings indicate that while ICSI has been transformative, particularly in addressing male infertility and facilitating fertilization, concerns persist regarding optimal sperm and embryo selection, potential genetic mutations, and long-term health implications. Ethical considerations surrounding the broad application of ICSI are also discussed. In conclusion, despite its effectiveness and success, ICSI is presented as a therapeutic method that is still evolving. The study emphasizes the importance of ICSI in infertility treatment by evaluating its historical progress, current status, and future prospects.

Historical Evolution and Techniques: The review traces the development of ICSI, beginning with early attempts. In 1988, efforts were made using human immature ova (MI stage) and sperm scheduled for discard. It was reported that insufficient force during sperm injection and a large amount of medium injected could hinder sperm decondensation. These early results suggested that injecting sperm into human ova might trigger pronucleus formation. In 1989, a technique called MIMIC (micro-insemination by microinjection into the cytoplasm) was reported, which involved directly injecting spermatozoa into the ooplasm (sometimes accidentally instead of the target perivitelline space – PVS). SUZI (subzonal sperm insemination) was another technique that facilitated sperm passage by injecting spermatozoa into the PVS. Due to the invasive nature of ICSI, the need to investigate the mechanism of fertilization and post-insemination survival was advocated. A report in 1991 compared SUZI and ICSI results for patients with severe teratozoospermia.

Following the successful human ICSI attempt in 1992, numerous studies have been published on its efficacy and improved therapeutic results. Comparisons with other methods like SUZI showed that ICSI, which directly injects a spermatozoon into the ovum, had a higher normal fertilization rate than SUZI, although the denaturation rate after insemination was higher in ICSI. PZD (zona drilling) was also considered an adjuvant method for achieving insemination, involving puncturing the zona pellucida (ZP) with a glass needle to help sperm entry. PZD was believed to have less effect on the fertilized ovum compared to techniques using chemical agents because it didn’t use them. A comparative study analyzing ICSI, SUZI, and PZD utilized ova from patients who had experienced failed SUZI attempts.

Reports were filed on successful ICSI attempts for infertility caused by the congenital bilateral absence of seminal ducts, using sperm collected via microsurgical epididymal sperm aspiration (MESA) or testicular sperm extraction (TESE). A subsequent report indicated that ICSI yielded high fertilization and implantation rates and did not increase the abnormality rate in ICSI-born infants. A review published in 1993 summarized ICSI-related phenomena and clinical results, including a Q&A section that highlighted the strong interest in ICSI at that time.

Mechanistic Aspects and Sperm Pretreatment: Ovum activation was reported to require the release of sperm factors. The calcium concentrations injected along with spermatozoa or during the puncture technique were thought to play an important role in ovum activation. Studies explored performing ICSI using calcium-free medium or a medium with EGTA (ethylene glycol tetraacetic acid), which chelates calcium. An artificial activation procedure using a calcium ionophore was reported to improve the pronucleus formation rate after ICSI. Calcium concentrations were found to differ depending on the puncture technique used during ICSI. Aspirating the ovum membrane during ICSI was suggested to establish calcium influx into the ooplasm and close contact between the sperm head and intracellular ovum calcium, potentially improving the fertilization rate. However, opinions differ on whether ovum membrane aspiration is necessary for successful ICSI.

Regarding sperm pretreatment before injection into the ooplasm, attempts to incubate spermatozoa in pentoxifylline or 2-deoxyadenosine did not show differences in fertilization and division rates compared to non-treated spermatozoa. Sperm immobilization later gained prominence as a pretreatment option. Scraping the sperm tail with an injection needle before injection resulted in an improved normal fertilization rate in ICSI. This technique is still widely used today. Damaging the sperm membrane was reported to immobilize the spermatozoon and introduce the centrosome into the ooplasm, inducing nuclear fusion after pronucleus formation. While laser-based techniques for immobilizing spermatozoa were developed, they reportedly did not gain significant traction. The most common technique for immobilization remains scraping the sperm tail with an injection needle.

Skepticism, Concerns, and Debates: Despite numerous reports on the efficacy and improved results of ICSI since 1992, skeptical views have also surfaced, alongside reports of potential abnormalities in fertilized ova caused by ICSI and negative effects on children born via ICSI. Debates during this period included discussions on fertilization rates in ICSI, reports and rebuttals regarding genetic abnormalities in ICSI-conceived babies, and the European Society of Human Reproduction and Embryology (ESHRE) views on the potential risks of spindle body damage from ICSI. Some researchers contended that the high risk of ICSI might arise from the fact that it allows fertilization of spermatozoa that cannot fertilize in vivo. Concerns were raised that the practical application of ICSI might have been premature. A series of reports warned that abnormalities related to ICSI might be linked to the use of polyvinylpyrrolidone (PVP) in the procedure. PVP is used to decrease sperm motility for ease of use during ICSI. PVP absorbed into the injection needle is injected into the ooplasm with the sperm. Reports suggested that PVP in the ooplasm delayed the start of calcium oscillations, reduced the post-ICSI fertilization rate by affecting sperm membrane and chromosomes, and increased the rate of chromosomal abnormalities. While some refuted these reports, stating that normal survival and fertilization rates were achieved even with PVP use, a series of articles insisted on investigating the long-term risks in children conceived with ICSI using PVP. Techniques for performing ICSI without PVP were also proposed.

Prognostic Investigations and Advanced Techniques: As several years passed since the rapid popularization of ICSI, results from prognostic investigations into the developmental and health status of children born after ICSI began to be published. These studies are considered critical for evaluating the outcomes in ICSI-born children, and the review presents major results from both proponents and skeptics of ICSI.

Advanced sperm selection techniques for ICSI were also explored. One example is HA-ICSI (hyaluronic acid-selected sperm ICSI), also referred to as physiological ICSI, which involves screening physiologically matured spermatozoa. Hyaluronic acid (HA) is a key component of the cumulus oophorus’s extracellular matrix, and mature spermatozoa have HA-binding sites on their membrane, unlike immature ones. This allows for screening mature sperm based on changes in their movement due to HA binding before they are subjected to ICSI. A Cochrane review cited in the document stated that differences in pregnancy, miscarriage, and childbirth rates between HA-ICSI and standard ICSI in previous randomized controlled trials (RCTs) were likely negligible or nonexistent.

Overall Conclusion and Future Perspective: The review concludes that both IVF and microscopic insemination (including ICSI) are considered essential components of infertility treatment today. Reproductive medicine has evolved gradually over many years while establishing its safety. Therefore, the need for continued gradual improvement while consistently confirming safety is highlighted.

The study was conducted at two IVF centers in Ho Chi Minh City, Vietnam. The primary objective of this secondary analysis was to investigate whether sperm morphology could serve as a biomarker to identify couples who would benefit more from Intracytoplasmic Sperm Injection (ICSI) compared to conventional In Vitro Fertilization (c-IVF) in terms of fertility outcomes, specifically for couples with infertility and normal total sperm count and motility. The original RCT protocol and main findings were reported elsewhere. The study was approved by a hospital ethics committee and registered on ClinicalTrials.gov (NCT03428919).

The study included 1064 couples who were randomly assigned to either the ICSI or c-IVF group, with 532 couples in each group. The analysis was performed based on the intention-to-treat principle, and the couple was used as the unit of analysis, rather than the oocyte. Baseline characteristics were comparable between the two groups. The couples were generally young, with adequate ovarian reserve and body mass index, about half had secondary infertility, and 90% were undergoing their first treatment attempt. Male partners had normal total sperm count and motility.

Sperm morphology was assessed using World Health Organization (WHO) criteria. The median proportion of sperm with normal morphology in both groups was 3%, with an interquartile range of 1–6%. The majority of couples had normal morphology less than 4%. Total sperm count was 63.6 (36.5–103.5) million/ml in the ICSI group and 68.5 (38.9–117.3) million/ml in the c-IVF group.

The researchers evaluated the effectiveness of ICSI versus c-IVF in relation to sperm morphology for four key outcomes: live birth rate (LBR), ongoing pregnancy rate, clinical pregnancy rate, and total fertilization failure (TFF). Statistical analysis included testing for interaction between sperm morphology (as a continuous variable) and the treatment effect using logistic regression, subgroup analysis based on sperm morphology quartiles, and restricted cubic spline analysis to evaluate the association between morphology and outcomes in each group.

Key Findings:

  • The live birth rate was 34.6% for ICSI (184/532) versus 31.2% for c-IVF (166/532).
  • Crucially, no significant interaction was found between sperm morphology and the treatment effect of ICSI versus c-IVF for any of the four outcomes: live birth, ongoing pregnancy, clinical pregnancy, and total fertilization failure. The p-values for interaction were 0.181, 0.153, 0.168, and 0.788, respectively.
  • Analysis using restricted cubic splines similarly found no evidence of interaction between sperm morphology and the treatment effect. The interaction figures showed that the effect of ICSI over c-IVF at different sperm morphology levels fluctuated around the “no effect” line, and the predicted outcomes for the two groups mostly overlapped at different sperm morphology levels.
  • Subgroup analysis based on sperm morphology quartiles also revealed no significant differences in the treatment effects of ICSI compared to c-IVF between the subgroups for any of the four outcomes.
  • The total fertilization failure rates were 6.4% in the c-IVF group and 5.5% in the ICSI group. No significant interaction or subgroup difference was found with morphology for TFF.

Discussion and Conclusion:

The authors state that a main strength of their study was investigating treatment-covariate interaction within a randomized setting, with available sperm morphology data for all participants, assessed using consistent WHO criteria. They also highlight considering morphology as a continuous outcome and investigating non-linear interactions.

However, limitations include the potential for the secondary analysis to be under-powered for some outcomes due to fewer events in subgroups, the exclusion of couples with previous poor fertilization rates which might limit generalizability, the lack of evaluation of other tests like DNA fragmentation index or acrosome reaction examination, and the use of sperm morphology from the first consultation instead of the day of randomization.

The authors conclude that their findings suggest sperm morphology has limited value as a biomarker to identify couples who would benefit more from ICSI over c-IVF in terms of live birth. This conclusion also applies to clinical pregnancy, ongoing pregnancy, and total fertilization failure. They note that these results align with other studies, including a recent meta-analysis on intrauterine insemination (IUI) which indicated a limited role for sperm morphology in predicting outcomes or treatment effects in both IUI and IVF settings.

Overall, the study indicates that for couples with normal total sperm count and motility, sperm morphology levels do not significantly influence the effectiveness of ICSI relative to conventional IVF.

The study involved a large retrospective cohort analysis conducted in a single third-level fertility center in Italy. A literature search was also performed on PubMed, EMBASE, and MEDLINE until July 2021, using keywords related to ICSI, IVF, and predictive factors, resulting in the selection of 96 relevant articles plus 14 additional theoretically important papers. The analysis considered factors such as female age, male age, male factor, and ovarian reserve. Original articles in English, Portuguese, or French were included, while reviews, meta-analyses, and inaccessible articles were excluded from the main review.

Semen analyses in the study cohort were performed according to the World Health Organization (WHO) manual available at the time of the ART cycle, with consistency maintained by the same laboratory which underwent regular quality controls and held an ESHRE quality certificate. Due to the wide time-frame of the study, three versions of the WHO manual (3rd, 4th, and 5th editions) were used. Methodological differences and changed reference ranges were introduced with each edition. The 3rd and 4th editions were considered together due to only minor changes. Definitions of oligozoospermia, asthenozoospermia, and teratozoospermia varied significantly between the previous editions (3rd/4th) and the 5th edition. For example, teratozoospermia was defined by sperm morphology <30% (3rd edition), <14% (4th edition), and <4% (5th edition).

Analysis of semen parameters according to the WHO manual edition used showed differences. Using the WHO 5th edition manual, higher semen volume (p < 0.001) and total sperm number (p < 0.001) were detected compared to previous editions, along with lower sperm concentration (p = 0.004), progressive motility (p < 0.001), and sperm morphology (p < 0.001). The median normal sperm morphology percentage was 6% (0.0–33.0) with previous editions and 3% (0.0–10.0) with the 5th edition. The different normal ranges led to a different frequency of sperm alterations being diagnosed, with a lower frequency of oligo-, astheno-, teratozoospermia, and OAT (oligo-astheno-teratozoospermia) diagnosed according to the WHO 5th edition compared to previous editions.

Considering the entire ART cohort, 5819 cycles were conventional IVF (26.4%) and 16,194 were ICSI (73.6%). The overall biochemical and clinical pregnancy rates were both around 20%. Among clinical pregnancies, the overall live birth rate was 63.3%.

In the study cohort, the fertilization rate was significantly higher in ICSI cycles (42.4 ± 39.7%) compared to IVF cycles (38.4 ± 49.2%) (p < 0.001).

Findings regarding Sperm Morphology as a Predictor:

  • In IVF cycles, fertilization rate was directly correlated with sperm concentration, total sperm number, progressive motility, and sperm morphology, regardless of the WHO manual edition used, although the strength of the correlation varied.
  • In ICSI cycles, fertilization rate was also directly correlated with sperm concentration, total sperm count, progressive motility, and sperm morphology, independently from the manual edition.
  • Multivariate analysis for ICSI cycles showed that only sperm morphology was included in the final model predicting the overall fertilization rate.
  • A Receiver Operating Characteristic (ROC) analysis using clinical pregnancy rate as a state variable and sperm morphology as a test variable in ICSI cycles identified a sperm morphology cut-off of 5.5% that could predict clinical pregnancy. This threshold had an Area Under the Curve (AUC) of 0.811 (p < 0.001) with a sensitivity of 72% and a specificity of 71%.
  • However, a ROC analysis using live birth rate as a state variable was not able to detect a sperm morphology threshold (AUC = 0.514, p = 0.550).
  • Considering only IVF cycles, the sperm morphology predictive ability for fertilization rate was confirmed only when the WHO manual’s 5th edition was used for semen analysis. The authors speculate that the last WHO manual (5th edition) might be more stringent and accurate in defining normal male fertility.

Findings regarding Sperm DNA Fragmentation (sDNAfrag / DFI) from the literature review:

  • The document presents conflicting reports from the literature regarding sDNAfrag.
  • Some literature reports indicate that high levels of sDNAfrag were not associated with fertilization rate, embryo quality rate, total number of blastocysts, and clinical pregnancy rate. DFI was also not associated with birth characteristics like birth weight and gestational age.
  • Conversely, one study noted a significantly higher implantation rate and clinical pregnancy rate with ICSI compared to IVF within a group with higher sDNAfrag.
  • The application of methods for selecting morphologically normal spermatozoa may result in the use of spermatozoa with lower sDNAfrag in ICSI.
  • It is believed that at the zygote stage, a mechanism exists for sperm DNA damage repair via oocyte DNA repair enzymes and antiapoptotic proteins, which appears dependent on the oocyte’s cytoplasmic and genomic quality. A study corroborated this, finding that sDNAfrag was a prognostic predictor of reduced CPR, LBR, and IR only in couples with reduced ovarian reserve but not in couples with normal ovarian reserve.
  • The fertilization rate did not appear to be affected by the presence of a higher DFI in ICSI groups compared to IVF groups.
  • LBR was described as significantly lower in IVF when DFI was >20% but not in ICSI.
  • The document includes a table summarizing purported relationships between Higher SDF and ART outcomes. This table lists correlations with lower FR, embryo quality rate, blastocyst rate, IR, CPR, and LBR. It also lists no correlations with FR, embryo quality rate, total blastocysts, CPR, gestational age, and birth weight. (Note: The table presents contradictory information regarding correlations with FR, embryo quality rate, total blastocysts, and CPR compared to the textual descriptions in and. This likely reflects conflicting findings across the reviewed literature).
  • The table also notes that TESA (Testicular Sperm Aspiration) is advised for recurrent implantation failures and recurrent pregnancy loss due to lower SDF in testicular sperm. SDF is increased in obstructive and secretory azoospermia.
  • Challenges in interpreting sDNAfrag studies include the use of different detection techniques (e.g., TUNEL, SCD, SCSA, DBD-FISH) and varying cut-off percentages. While numerous cut-offs for DFI have been reported without an absolute upper limit defining unsuccessful pregnancy, recent efforts suggest a consensual cut-off of ≥ 20% for the TUNEL assay, though caution in interpretation is advised.

The authors indicate that the final model predicting overall fertilization rate in ICSI cycles included only sperm morphology. In contrast, for IVF cycles, multiple semen parameters seemed to influence fertilization rate using previous WHO editions, but these disappeared when co-variates were considered, suggesting the 5th edition might be more accurate. A correlation between DFI and sperm morphology was observed only in motile sperm after swim-up, and DFI analysis after swim-up is suggested if whole semen DFI is ≥15%.

This synthesis discusses the impact of intracytoplasmic sperm injection (ICSI) compared to conventional in vitro fertilization (cIVF) on the reproductive outcomes of couples with non-male factor infertility, particularly focusing on frozen-thawed embryo transfer (FET) cycles, and incorporates findings on sperm parameters and neonatal outcomes from other related sources.

Introduction and Background

Intracytoplasmic sperm injection (ICSI) is an assisted reproductive technology (ART) that involves the injection of a single spermatozoon into a mature oocyte. It was first successfully reported in humans in 1992, and since then, its use has dramatically increased globally. ICSI was initially introduced as the most effective solution for severe male infertility. However, its utilization has surged far beyond severe male factor cases, with a substantial increase observed specifically in couples diagnosed with non-male factor infertility. For example, in the US, ICSI use in non-male factor infertility cases rose from 15.4% in 1996 to 66.9% in 2012. Data from the Latin American Registry showed ICSI being used in four out of five cycles for couples without male factor infertility. While its application is widespread in some regions, its use remains relatively low in China compared to Europe and the USA.

Despite its success in addressing male infertility, the application of ICSI in couples with non-male factor infertility has been a subject of considerable debate. The rationale often cited for using ICSI in these cases includes preventing total fertilization failure (TFF) and increasing fertilization rates (FR). However, ICSI is a sophisticated and invasive technique that carries potential risks, such as damage to the oocyte membrane or organelles, which could lead to reduced embryonic development potential and potentially increase the risk of birth defects.

Numerous studies have investigated the efficacy of ICSI in non-male factor infertility, often yielding conflicting results. Much of the existing evidence comes from studies on fresh embryo transfer cycles following ovarian stimulation. There has been limited evidence regarding ICSI’s impact on reproductive outcomes specifically in couples with non-male factor infertility undergoing frozen-thawed embryo transfer (FET) treatment. The study by Zhang et al. titled “The impact of intracytoplasmic sperm injection versus conventional in vitro fertilization on the reproductive outcomes of couples with non‑male factor infertility and frozen‑thawed embryo transfer cycles” aims to address this gap by focusing on FET cycles.

Findings from the Zhang et al. Study (Focus on FET)

The study by Zhang et al. was a retrospective cohort study involving 10,143 FET cycles from 6206 couples with non-male factor infertility at the Third Affiliated Hospital of Zhengzhou University between 2016 and 2022. Patients were categorized into two groups based on whether the transferred embryos were conceived via ICSI or cIVF. The study compared clinical and neonatal outcomes between these groups.

The main findings indicated that ICSI was not associated with improved clinical outcomes compared to cIVF in couples with non-male factor infertility undergoing FET. While a subgroup analysis in this study showed a slight improvement in live birth rate with ICSI for this population, the overall regression analysis did not demonstrate any general improvement in reproductive outcomes.

Regarding neonatal outcomes, when considering single live births, the results were consistent with previous randomized controlled trials (RCTs). However, a notable finding specific to this study was that ICSI was associated with lower birthweight and shorter birth length when twins were born. Consequently, ICSI was linked to a higher low-birth-weight rate in twin pregnancies. The authors concluded that infertile women with twin pregnancies should be informed of the potential for lower birthweight and length if their oocytes were inseminated with ICSI.

The study acknowledged limitations, including its retrospective design which could introduce selection bias (though propensity score matching was used to mitigate this). The specific causes of non-male factor infertility were not detailed, which means the results apply to a broader population but limit subgroup analysis based on specific female factors. The study focused on primary clinical outcomes (pregnancy, miscarriage, live birth) and did not compare early reproductive outcomes like embryo quality or fertilization rate in detail within the FET context. Long-term follow-up of children was also not conducted.

Broader Evidence on ICSI in Non-Male Factor Infertility (Drawing from other sources)

Other sources provide broader perspectives on ICSI in non-male factor infertility, often based on fresh embryo transfer cycles.

A systematic review and meta-analysis by Yang et al. included 18 RCTs comparing ICSI and IVF in women with non-male factor infertility. This comprehensive review aimed to provide updated evidence due to conflicting results in previous reviews and the availability of new RCTs. It included studies randomizing either patients or sibling oocytes.

The Yang et al. meta-analysis found that ICSI did not improve Live Birth Rate (LBR) compared to IVF. They also found no significant difference in Clinical Pregnancy Rate (CPR) or Miscarriage Rate (MR). While ICSI was shown to reduce the risk of TFF and increase FR per oocyte inseminated/injected overall, the review noted that the apparent reduction in TFF was not evident when only studies randomizing patients (rather than sibling oocytes) were analyzed. The difference in fertilization rate calculations (per oocyte retrieved vs. per oocyte inseminated/injected) was explained by the fact that ICSI only injects mature oocytes, whereas cIVF exposes both mature and some immature oocytes to sperm, with some immature oocytes maturing in vitro during the process. This means that while ICSI might show a higher fertilization rate among the selected, injected oocytes, the overall rate among all retrieved oocytes might not differ significantly. The authors also calculated that it would require approximately 50 additional ICSI cycles to avoid one instance of TFF compared to IVF, arguing against routine use of ICSI solely for TFF reduction.

The “Key message” from the Yang et al. meta-analysis explicitly states that ICSI is not associated with lower fertilization failure and other reproductive outcomes in patients with non-male factor infertility. It concludes that, considering the cost and safety of ICSI, there is no evidence to support its routine use in these populations. This aligns with previous well-designed RCTs cited elsewhere, which also showed that ICSI did not improve LBR or clinical outcomes in couples with non-severe male factor infertility after adjusting for confounding factors.

The debate continues in specific subgroups, such as women of advanced maternal age or those with poor ovarian response. While some studies suggested ICSI might improve outcomes in these groups (e.g., higher FR and more top-quality embryos in advanced age in one small study), others showed comparable or even reduced LBR with ICSI. The Zhang et al. study, in its subgroup analysis based on female age and oocyte number (as a proxy for ovarian response), found no improved outcomes with ICSI.

Sperm Parameters and Predictive Value

Another relevant source explored whether sperm parameters can predict ART success. While various sperm parameters, such as progressive motility and morphology, are assessed, their ability to predict outcomes and guide the choice between ICSI and IVF, especially in cases without severe male factor infertility, appears limited.

A secondary analysis of a large RCT by Pham et al., specifically examining couples with infertility and normal total sperm count and motility, investigated whether sperm morphology could serve as a biomarker to identify those who would benefit more from ICSI over cIVF. Using WHO 2010 criteria for morphology assessment, the study concluded that sperm morphology had limited value as a biomarker for predicting improvements in live birth, ongoing pregnancy, clinical pregnancy, or TFF when choosing ICSI over cIVF in this population. This supports the finding from the Yang et al. meta-analysis that ICSI does not significantly reduce TFF when considering patient-level randomization, even across different levels of sperm morphology in the Pham et al. study [108, Figure 2A].

Sperm DNA fragmentation (sDNAfrag) is another parameter discussed. Some evidence suggests that higher sDNAfrag might negatively impact outcomes in IVF more than in ICSI, possibly due to the oocyte’s DNA repair capacity. However, the Pham et al. study did not evaluate sDNAfrag, and the overall predictive value of sDNAfrag is still debated, with no universally agreed-upon threshold for defining unsuccessful pregnancy.

Neonatal Health and Long-Term Outcomes

Concerns about the potential impact of ICSI on the health and development of ICSI-born children have been raised since the technique’s introduction. The Zhang et al. study’s finding of lower birthweight and length specifically in twin pregnancies conceived via ICSI is a significant result in the context of FET.

The broader literature presents conflicting reports on the prognosis of ICSI-born children. Some studies have reported that ICSI-born children show no significant differences in outcomes such as premature birth rate, newborn weight (though Zhang et al. found differences in twins), major malformations, chromosomal abnormalities, or psychological/motor/intellectual development compared to naturally conceived or IVF-conceived children at various ages up to 8 years. However, debates about the health and development of these children are ongoing, with some studies reporting positive results and others expressing concerns. The necessity for more multi-center, multi-regional, and multi-national long-term follow-up investigations is emphasized to accurately assess potential risks. The Yang et al. meta-analysis was limited in its ability to analyze congenital disabilities and neonatal growth due to a lack of sufficient data in the included RCTs.

Limitations and Future Research

The sources collectively highlight the complexity and ongoing questions surrounding ICSI use in non-male factor infertility. Limitations across studies include:

  • Retrospective designs in some studies.
  • Potential underpowering for analyzing less common outcomes or subgroups.
  • Variations in study protocols and participant characteristics contributing to heterogeneity in meta-analyses.
  • Lack of detailed information on specific female infertility etiologies in some studies.
  • Limited data on early reproductive outcomes (like embryo quality) and long-term follow-up of children.
  • Insufficient data specifically on FET cycles in systematic reviews focusing on non-male factor infertility.

Future research recommendations include conducting high-quality RCTs with large sample sizes to confirm findings. More attention is needed on the cost-effectiveness of ICSI. Long-term follow-up studies of children conceived via ICSI in various infertility scenarios are crucial for assessing health and developmental outcomes. Research specifically investigating the impact of ICSI on reproductive and neonatal outcomes in different types of female factor infertility, especially within FET cycles, is also needed.

Conclusion and Clinical Implications

Based on the evidence from these sources, including a large retrospective study focused on FET cycles, a systematic review and meta-analysis of RCTs, and analyses of sperm parameters, there is a general consensus that routine use of ICSI is not supported for couples with non-male factor infertility. ICSI does not appear to improve live birth rates or overall clinical outcomes in this population. While ICSI might affect fertilization rates per injected oocyte or show a trend toward reducing TFF in some study designs, these benefits do not translate into improved live birth rates. Considering the higher cost and invasiveness of ICSI compared to cIVF, and the lack of clear benefit in clinical outcomes for non-male factor infertility, it is generally recommended to avoid its routine use.