Estimating the impact of bias in causal epidemiological studies: the case of health outcomes following assisted reproduction.

Researchers interested in causal questions must deal with two sources of error: random error (random deviation from the true mean value of a distribution), and bias (systematic deviance from the true mean value due to extraneous factors). For some causal questions, randomization is not feasible, and observational studies are necessary. Bias poses a substantial threat to the validity of observational research and can have important consequences for health policy developed from the findings. The current piece describes bias and its sources, outlines proposed methods to estimate its impacts in an observational study, and demonstrates how these methods may be used to inform debate on the causal relationship between medically assisted reproduction (MAR) and health outcomes, using cancer as an example. In doing so, we aim to enlighten researchers who work with observational data, especially regarding the health effects of MAR and infertility, on the pitfalls of bias, and how to address them. We hope that, in combination with the provided example, we can convince readers that estimating the impact of bias in causal epidemiologic research is not only important but necessary to inform the development of robust health policy and clinical practice recommendations.

Biosimilars versus the originator of follitropin alfa: Randomized controlled trials are still the best way to evaluate their comparative effectiveness in assisted reproduction.

Biosimilars of follitropin alfa have been introduced in many countries as more affordable alternatives to the reference product for patients undergoing ovarian stimulation for assisted reproductive technology cycles. A recent meta-analysis, by reviewing available evidence originating from randomised controlled trials, has shown that based on the best available evidence, biosimilars of follitropin alfa are associated with lower live birth, ongoing and clinical pregnancy rates compared to the reference product. A subsequently published opinion paper challenges the methodology and results of this meta-analysis and suggests that these data should be ignored. In the present paper, it is clearly demonstrated why this criticism is largely unfounded and in stark contradiction with basic principles of evidence-based medicine. Furthermore, it is presented why the results of this meta-analysis provide the best available evidence to date and therefore the base that should inform clinical practice and, importantly, stimulate further research.

Individual participant data meta-analysis of trials comparing frozen versus fresh embryo transfer strategy (INFORM): a protocol.

INTRODUCTION: Existing randomised controlled trials (RCTs) comparing a freeze-all embryo transfer strategy and a fresh embryo transfer strategy have shown conflicting results. A freeze-all or a fresh transfer policy may be preferable for some couples undergoing in-vitro fertilisation (IVF), but it is unclear which couples would benefit most from each policy, how and under which protocols. Therefore, we plan a systematic review and individual participant data meta-analysis of RCTs comparing a freeze-all and a fresh transfer policy. METHODS AND ANALYSIS: We will search electronic databases (Medline, Embase, PsycINFO and CENTRAL) and trial registries (ClinicalTrials.gov and the International Clinical Trials Registry Platform) from their inception to present to identify eligible RCTs. We will also check reference lists of relevant papers. The search was performed on 23 September 2020 and will be updated. We will include RCTs comparing a freeze-all embryo transfer strategy and a fresh embryo transfer strategy in couples undergoing IVF. The primary outcome will be live birth resulting from the first embryo transfer. All outcomes listed in the core outcome set for infertility research will be reported. We will invite the lead investigators of eligible trials to join the Individual participant data meta-analysis of trials comparing frozen versus fresh embryo transfer strategy (INFORM) collaboration and share the deidentified individual participant data (IPD) of their trials. We will harmonise the IPD and perform a two-stage meta-analysis and examine treatment-covariate interactions for important baseline characteristics. ETHICS AND DISSEMINATION: The study ethics have been granted by the Monash University Human Research Ethics Committee (Project ID: 30391). The findings will be disseminated via presentations at international conferences and publication in peer-reviewed journals. PROSPERO REGISTRATION NUMBER: CRD42021296566.

Pro: Fresh versus frozen embryo transfer. Is frozen embryo transfer the future?

Embryo cryopreservation has been an integral part of ART for close to 40 years and vitrification has boosted overall ART efficacy and safety. Recently, there has been a vivid scientific discussion on whether elective cryopreservation of all embryos (freeze-all) should be pursued for most patients, with a fresh embryo transfer taking place only in selected cases. In terms of efficacy, the available evidence suggests that the freeze-all strategy leads to higher live birth rates after the first embryo transfer compared to the conventional strategy in high responders, while there is no difference in normal responders. There is no evidence to suggest that the freeze-all strategy is inferior to the conventional strategy of fresh transfer when comparing cumulative live birth rates using data from all available randomized controlled trials. The incidence of ovarian hyperstimulation syndrome is significantly reduced in the freeze-all policy. However, regarding obstetric complications and neonatal outcomes, the evidence suggests that each strategy is associated with certain risks and, therefore, there is no approach that could be unequivocally accepted as safer. Similarly, limited evidence does not support the notion that patients would be universally against freeze-all owing to the inevitable delay in pregnancy achievement. Finally, the cost-effectiveness of freeze-all is likely to vary in different settings and there have been studies supporting that this policy can be, under certain conditions, cost-effective. Adoption of the freeze-all policy can also allow for more flexible treatment strategies that have the potential to increase efficacy, reduce cost and make treatment easier for patients and clinics. Importantly, freeze-all does not require the use of any experimental technologies, further training of personnel or the costly acquisition of new equipment. For these reasons, transitioning to the freeze-all policy for most patients appears to be the next logical step in ART.

Optimising Follicular Development, Pituitary Suppression, Triggering and Luteal Phase Support During Assisted Reproductive Technology: A Delphi Consensus.

Background: A Delphi consensus was conducted to evaluate global expert opinions on key aspects of assisted reproductive technology (ART) treatment. Methods: Ten experts plus the Scientific Coordinator discussed and amended statements plus supporting references proposed by the Scientific Coordinator. The statements were distributed via an online survey to 35 experts, who voted on their level of agreement or disagreement with each statement. Consensus was reached if the proportion of participants agreeing or disagreeing with a statement was >66%. Results: Eighteen statements were developed. All statements reached consensus and the most relevant are summarised here. (1) Follicular development and stimulation with gonadotropins (n = 9 statements): Recombinant human follicle stimulating hormone (r-hFSH) alone is sufficient for follicular development in normogonadotropic patients aged <35 years. Oocyte number and live birth rate are strongly correlated; there is a positive linear correlation with cumulative live birth rate. Different r-hFSH preparations have identical polypeptide chains but different glycosylation patterns, affecting the biospecific activity of r-hFSH. r-hFSH plus recombinant human LH (r-hFSH:r-hLH) demonstrates improved pregnancy rates and cost efficacy versus human menopausal gonadotropin (hMG) in patients with severe FSH and LH deficiency. (2) Pituitary suppression (n = 2 statements): Gonadotropin releasing hormone (GnRH) antagonists are associated with lower rates of any grade ovarian hyperstimulation syndrome (OHSS) and cycle cancellation versus GnRH agonists. (3) Final oocyte maturation triggering (n=4 statements): Human chorionic gonadotropin (hCG) represents the gold standard in fresh cycles. The efficacy of hCG triggering for frozen transfers in modified natural cycles is controversial compared with LH peak monitoring. Current evidence supports significantly higher pregnancy rates with hCG + GnRH agonist versus hCG alone, but further evidence is needed. GnRH agonist trigger, in GnRH antagonist protocol, is recommended for final oocyte maturation in women at risk of OHSS. (4) Luteal-phase support (n = 3 statements): Vaginal progesterone therapy represents the gold standard for luteal-phase support. Conclusions: This Delphi consensus provides a real-world clinical perspective on the specific approaches during the key steps of ART treatment from a diverse group of international experts. Additional guidance from clinicians on ART strategies could complement guidelines and policies, and may help to further improve treatment outcomes.

Biosimilar recombinant follitropin alfa preparations versus the reference product (Gonal-F®) in couples undergoing assisted reproductive technology treatment: a systematic review and meta-analysis.

BACKGROUND: Live birth has increasingly been identified as the standard clinical approach to measure the success of medically assisted reproduction (MAR). However, previous analyses comparing biosimilar preparations of follitropin alfa versus the reference product (GONAL-f®, Merck KGaA, Darmstadt, Germany or GONAL-f® RFF; EMD Serono, Inc., Rockland, MA), have had insufficient power to detect differences in clinically meaningful outcomes such as live birth. METHODS: Medline, Embase, the Cochrane Library, Web of Science and clinical trial registries were searched for randomised controlled trials (RCTs) and conference abstracts comparing biosimilar follitropin alfa versus the reference product in controlled ovarian stimulation (COS) cycles published before 31 October 2020. Only studies in humans and publications in English were included. Retrieved studies were screened independently by two authors based on titles and abstracts, and then by full text. INCLUSION CRITERIA: RCTs comparing follitropin alfa biosimilar preparations with the reference product in infertile patients of any age, with any type of infertility for any duration, undergoing COS for the purposes of MAR treatment (including frozen cycles). The primary outcome was live birth. Combined data for biosimilar preparations were analysed using a fixed-effects model. RESULTS: From 292 unique records identified, 17 studies were included in the systematic review, representing five unique RCTs that were included in the meta-analysis. Rates of live birth (RR = 0.83, 95% CI 0.71, 0.97; 4 RCTs, n = 1881, I2 = 0%), clinical pregnancy (RR = 0.82, 95% CI 0.72, 0.94; 4 RCTs, n = 2222, I2 = 0%) and ongoing pregnancy (RR = 0.81, 95% CI 0.68, 0.96; 4 RCTs, n = 1232, I2 = 0%) were significantly lower with biosimilar preparations versus the reference product. Rates of cumulative live birth and cumulative clinical pregnancy were also significantly lower with biosimilars versus the reference product. There was high risk of publication bias. CONCLUSIONS: This meta-analysis included data from RCTs evaluating the efficacy and safety of the biosimilar follitropin alfa preparations and demonstrated lower probability of live birth and pregnancy (ongoing and clinical) in couples treated with biosimilar preparations compared with the reference product. This study provides more insight into the differences between biosimilar r-hFSH preparations and the reference product than previously reported. TRIAL REGISTRATION: Registration number: CRD42019121992 .

Female age is associated with the optimal number of oocytes to maximize fresh live birth rates: an analysis of 256,643 fresh ART cycles.

RESEARCH QUESTION: What is the optimal number of oocytes retrieved at which maximum live birth rate is observed after fresh autologous assisted reproductive technology (ART) cycles for women of different ages? DESIGN: Retrospective cohort study of all fresh autologous ART aspiration cycles (n = 256,643) undertaken in Australia and New Zealand between 2009 and 2015. Primary outcome measure was live birth rate (LBR) (delivery of at least one liveborn baby at 20 weeks' gestation or over per fresh aspiration cycle). Cycles were grouped according to female age (<30, 30-34, 35-49, 40-44 and ≥45 years) and ovarian response (one to three, four to nine, 10-14, 15-19, 20-25 and ≥25 oocytes). Secondary outcome was incidence of ovarian hyperstimulation syndrome (OHSS) requiring hospitalization. RESULTS: At different oocyte yields, LBR per fresh aspiration cycle peaked and then declined at, depending on female age: <30 years: six to 11 oocytes (LBR 31-34%); 30-34 years: 11-16 oocytes (LBR 29-30%); 35-39 years: nine to 17 oocytes (LBR 21-24%); and 40-44 years: 15-17 oocytes (LBR 11-12%). The incidence of OHSS increased significantly with the number of oocytes retrieved, from 1.2% with 15 oocytes retrieved to 9.3% with 30 or more oocytes retrieved (P < 0.001). CONCLUSION: The optimal number of oocytes at which maximum LBR was observed in a fresh aspiration cycle was highly dependent on age. Because of the observational nature of the results, a cause-effect relationship between the number of oocytes retrieved and LBR should not be assumed; evidence from well-designed randomized control trials is required before clinical advice can be suggested.

Is there an optimal number of oocytes retrieved at which live birth rates or cumulative live birth rates per aspiration are maximized after ART? A systematic review.

The association between the number of oocytes retrieved and fresh live birth rate (LBR) or cumulative LBR (CLBR), and whether an optimal number of oocytes are retrieved when LBR or CLBR are maximized, are highly relevant clinical questions; however published results are conflicting. A systematic review of all eligible studies (n = 16) published until January 2020 on MEDLINE, Embase, Scopus, CINAHL and Web of Science was conducted. Five studies evaluated only LBR from fresh cycles, five studies evaluated only CLBR from stimulated cycles and six evaluated both. A marked difference was observed between the oocyte yields at which LBR and CLBR were reportedly maximized in the individual studies. On the basis of nine studies, the optimal number of oocytes at which fresh LBR seems to be maximized is proposed to be between 12 and 18 oocytes (15 oocytes was the most common suggestion). On the other hand, CLBR continues to increase with the number of oocytes retrieved. This is the first systematic review on the topic, and it suggests that the retrieval of 12-18 oocytes is associated with maximal fresh LBR, whereas a continuing positive association is present between the number of oocytes retrieved and CLBR.

Association between body mass index and oocyte maturation in patients triggered with GnRH agonist who are at high risk for severe ovarian hyperstimulation syndrome: an observational cohort study.

RESEARCH QUESTION: Is body-mass index (BMI) associated with oocyte maturation in women at high risk for developing severe ovarian hyperstimulation syndrome (OHSS) who are triggered with gonadotrophin releasing hormone (GnRH) agonist? DESIGN: Prospective observational cohort study. A total of 113 patients at high risk for severe OHSS (presence of at least 19 follicles ≥11 mm) pre-treated with gonadotrophin releasing hormone (GnRH) antagonists and recombinant FSH were administered 0.2 mg triptorelin to trigger final oocyte maturation. Patients were classified in two groups depending on their BMI: ΒΜΙ less than 25 kg/m2 (n = 72) and ΒΜΙ 25 kg/m2 or over (n = 41). Baseline, ovarian stimulation and embryological characteristics, as well as luteal-phase hormone profiles, were compared in patients classified into the two BMI groups. The main outcome measure was the number of mature oocytes. RESULTS: A significantly higher number of mature (metaphase II) oocytes (19 [18-21] versus 16 [13-20], P = 0.029) was present in women with BMI less than 25 kg/m2 compared with those with BMI 25 kg/m2 or greater. The number of retrieved oocytes, the number of fertilized oocytes, oocyte retrieval, maturation and fertilization rates were similar in the two groups. A significantly higher dose of recombinant FSH was required for patients with BMI 25 kg/m2 or greater compared with patients with BMI less than 25 kg/m2 (1875 [1650-2150] IU versus 1650 [1600-1750] IU, P = 0.003) and the two groups displayed different luteal phase hormonal profiles. CONCLUSIONS: Among women at high risk for developing severe OHSS who are triggered with a standard dose (0.2 mg) of the GnRH agonist triptorelin, women with BMI 25 kg/m2 or greater had significantly fewer mature oocytes, required a higher total dose of recombinant FSH compared with women with BMI less than 25 kg/m2.

Fine-tuning blastocyst selection based on morphology: a multicentre analysis of 2461 single blastocyst transfers.

RESEARCH QUESTION: Which blastocyst morphology parameter is associated with live birth after controlling for female age and endometrial receptivity? DESIGN: Retrospective study including fresh single blastocyst transfers (n = 2461) where the value of serum progesterone on day of human chorionic gonadotrophin trigger (PdHCG) was available. Generalized estimating equation regression models evaluated the independent effects of developmental stage (DevSt), inner cell mass (ICM) and trophectoderm grade on live birth rates while controlling for the confounding effects of female age and PdHCG. RESULTS: DevSt was strongly associated with the probability of live birth (P < 0.0001) independently of female age (odds ratio [OR] 0.89, 95% confidence interval [CI] 0.87-0.91) and PdHCG (OR 0.80, 95% CI 0.74-0.87). For full blastocysts, expanded blastocysts and hatching blastocysts, addition of ICM and trophectoderm grading in the multivariable analysis suggested that besides female age (OR 0.92, 95% CI 0.90-0.94) and PdHCG (OR 0.80, 95% CI 0.73-0.87), only DevSt (P = 0.001) and trophectoderm quality (P = 0.004) were independent predictors of live birth, while the predictive capacity of ICM was no longer significant. The mean probability of live birth was highest for AA blastocysts (35.0%), followed by BA blastocysts (31.2%) and AB blastocysts (27.7%). CONCLUSION: This large study analyses for the first time the independent role of blastocyst morphology in predicting live birth while controlling for female age and PdHCG. Its findings suggest that DevSt and then trophectoderm grade are stronger predictors of live birth over ICM grade when selecting a single blastocyst for transfer.

Is there an association between oocyte number and embryo quality? A systematic review and meta-analysis.

This systematic review and meta-analysis determined the association between aspirated after ovarian stimulation and top/good quality embryos obtained in women undergoing ovarian stimulation for IVF/intracytoplasmic sperm injection (ICSI). MEDLINE, EMBASE, Scopus, CINAHL and Web of Science were searched for English-language publications on top/good-quality embryos at cleavage (day 2/3) and/or blastocyst (day 5/6) developmental stages, up to 18 November 2017. Twenty-eight studies (three prospective and 25 retrospective) reporting data on 291,752 assisted reproductive technology (ART) cycles were considered eligible. We confirmed a strong positive association between oocytes retrieved and top/good-quality day 2/3 embryos (weighted correlation coefficient [rw] = 0.791), day 5/6 embryos (rw = 0.901), metaphase II oocytes (rw = 0.988), oocytes exhibiting two pronuclei (rw = 0.987) and euploid embryos (rw = 0.851); P < 0.001 for all correlations (evaluated in subsets of the 17 studies). Data from 5657 cycles showed that the group with the most oocytes aspirated had the most top/good-quality day 2/3 embryos (pooled standardized mean differences (high [>15] versus low [<4] 1.91, 95% confidence interval [CI] 1.05-2.77, P < 0.0001; high versus medium [4-15] 1.15, 95% CI 0.74-1.55, P < 0.0001; medium versus low 1.41, 95% CI 0.79-2.03, P < 0.0001). Individual participant meta-analysis would enable accurate determination of these associations and other outcomes.

The number of oocytes associated with maximum cumulative live birth rates per aspiration depends on female age: a population study of 221 221 treatment cycles.

STUDY QUESTION: What is the number of oocytes where the maximum cumulative live birth rate per aspiration (CLBR) is observed during ART in women of different ages? SUMMARY ANSWER: The maximum CLBR was observed when around 25 oocytes were retrieved in women between 18-35 years of age, around 9 oocytes in women more than 45 years of age and continued to increase beyond 30 oocytes in women between 36-44 years of age. WHAT IS KNOWN ALREADY: The live birth rate per fresh or frozen/thaw embryo transfer (FET) procedure has traditionally been the main measure of ART success. However, with the introduction of highly efficient embryo cryopreservation methods, CLBR encompassing live delivery outcomes from the fresh and all subsequent FET following a single ovarian stimulation and oocyte collection is increasingly viewed as a more meaningful measure of treatment success. There is evidence suggesting that larger oocyte yields are associated with increased likelihood of cumulative live birth per aspiration. Whether this association is the same across female ages has not yet been properly investigated. STUDY DESIGN, SIZE, DURATION: This is a large retrospective population-based cohort study using data from the Australian and New Zealand Assisted Reproduction Database (ANZARD). ANZARD contains information from all ART treatment cycles carried out in all fertility centres in Australia and New Zealand. Overall, 221 221 autologous oocyte aspiration cycles carried out between January 2009 to December 2015 were included in the analysis. PARTICIPANTS/MATERIALS, SETTING, METHODS: Cumulative live birth per aspiration was defined as at least one liveborn baby at ≥20 weeks gestation resulting from an ART aspiration cycle, including all fresh and FET resulting from the associated ovarian stimulation, until one live birth occurred or all embryos were used. Cycles where no oocytes were retrieved were excluded from analysis as there is no possibility of live birth. Analyses of data were performed using generalized estimating equations to account for the clustered nature of data (multiple cycles undertaken by a woman). Univariate and multivariable regression analysis was performed to identify and adjust for factors known to independently affect cumulative live birth per aspiration. An interaction term between female age and the number of oocytes retrieved was included to assess whether the age of the women was associated with a different optimal number of oocytes to achieve at least one live birth from an aspiration cycle (i.e. the effect-modifying role of female age). The likelihood of cumulative live birth per aspiration was calculated as odds ratios (ORs) with 95% CI. MAIN RESULTS AND THE ROLE OF CHANCE: The median number of oocytes retrieved was 7 (interquartile range, 4-12) and median age of patients was 36 (interquartile range, 33-40). The overall CLBR was 32.2%. The results from the multivariable regression analysis showedthat the number of oocytes retrieved remained a significant predictor (P < 0.001) of cumulative live birth per aspiration after adjusting for female age, parity and cycle count. Compared to the reference group of 10-14 oocytes retrieved, the adjusted odds for cumulative live birth per aspiration increased with the number of oocytes retrieved: 1-3 oocytes, 0.21 (95% CI, 0.20-0.22); 4-9 oocytes, 0.56 (95% CI, 0.55-0.58); 15-19 oocytes, 1.38 (95% CI, 1.34-1.43); 20-24 oocytes, 1.75 (95% CI, 1.67-1.84); and 2.10 (95% CI, 1.96-2.25) with more than 25 oocytes. After stratifying by female age group, the rate of increase in CLBR per additional oocyte retrieved was lower in the older age groups, indicating that higher oocyte yields were more beneficial in younger women. CLBR of patients in the <30 years and 30-34 years age groups appeared to reach a plateau (with only minimal increase in CLBR per additional oocyte retrieved) after retrieval of 25 oocytes at 73% and 72%, respectively, while CLBR of patients in the 35-39 years and 40-44 years age groups continued to increase with higher oocyte yields, reaching 68% and 40%, respectively, when 30 or more oocytes were retrieved. CLBR of patients aged 45 years and above remained consistently below 5%. Findings suggest that the number of oocytes retrieved where CLBR appears to be maximized is around 25 in women between 18-35 years, more than 30 in women between 36-44 years and around 9 in women 45 years and older. However, results for women aged 45 years and older may not be as robust due to the relatively small sample size available in this age group. LIMITATIONS, REASONS FOR CAUTION: As with all large retrospective database studies, there are potential confounders that cannot be accounted for. Despite the current study being based on complete ascertainment of ART cycles across two countries, ovarian stimulation protocols, oocyte quality parameters and a number of important patient characteristics are not collected by ANZARD. Additionally, a small number of cycles were available for women over 45 years yielding more than 15 oocytes, making these estimates unreliable. WIDER IMPLICATIONS OF THE FINDINGS: The results from this study demonstrate that the number of oocytes retrieved where the maximum CLBR is observed during ART is dependent on female age. This provides information for clinicians and patients to understand the modifying effect of age on the number of oocytes retrieved and the likelihood of success with ART. STUDY FUNDING/COMPETING INTEREST(S): No external funding was used for this study. The Fertility Society of Australia funds the National Perinatal Epidemiology and Statistics Unit to manage ANZARD and conduct national reporting of ART in Australia and New Zealand. Associate Professor Georgina Chambers (G.C.) is employed by the University of New South Wales (UNSW) and is director of the National Perinatal Epidemiology and Statistics Unit at UNSW. G.C. was also a paid member of the Australian governments Medicare Benefits Scheme taskforce on assisted reproductive technologies in 2017.

A Review of Second- and Third-line Infertility Treatments and Supporting Evidence in Women with Polycystic Ovary Syndrome.

In clomiphene-citrate-resistant anovulatory women with polycystic ovary syndrome (PCOS) and no other infertility factors, either metformin combined with clomiphene citrate or gonadotrophins could be used as a second-line pharmacological therapy, although gonadotrophins are more effective. Gonadotrophins could also be used as a second-line pharmacological therapy in anovulatory women with PCOS and clomiphene-citrate-failure. Laparoscopic ovarian surgery can also be used as a second-line therapy for ovulation induction in anovulatory women with clomiphene-citrate-resistant PCOS and no other infertility factors. The usefulness of letrozole as a second-line pharmacological treatment for ovulation induction in clomiphene-citrate-resistant women with PCOS requires further research. In terms of improving fertility, both pharmacological anti-obesity agents and bariatric surgery should be considered an experimental therapy in anovulatory women with PCOS and no other infertility factors. Where first- or second-line ovulation induction therapies have failed, in vitro fertilization (IVF)/ intracytoplasmic sperm injection (ICSI) could be offered as a third-line therapy in women with PCOS in the absence of an absolute indication for IVF/ICSI. For women with PCOS undergoing IVF/ICSI treatment, the gonadotropin-releasing hormone (GnRH) antagonist protocol is preferred and an elective frozen embryo transfer strategy could be considered. In assisted conception units with sufficient expertise, in-vitro maturation (IVM) of oocytes could be offered to women with PCOS.

Is more better? A higher oocyte yield is independently associated with more day-3 euploid embryos after ICSI.

STUDY QUESTION: Is the number of oocytes retrieved after ovarian stimulation for ICSI independently associated with the number of day-3 euploid embryos (EE)? SUMMARY ANSWER: A larger oocyte yield is independently associated with more day-3 EE, although the expected benefit decreases significantly with advancing age. WHAT IS KNOWN ALREADY: Although traditionally ovarian stimulation aims at collecting more than one oocyte in order to increase the chance of pregnancy, there is evidence suggesting that excessive ovarian response leads to lower live birth rates. Whether a larger oocyte yield after ovarian stimulation is associated with the genetic composition of the resulting embryos and therefore with their reproductive potential is still largely unknown. STUDY DESIGN, SIZE, DURATION: This is a multi-centered retrospective cohort study analyzing 724 cycles of preimplantation genetic testing for aneuploidy (PGT-A) cycles using day-3 biopsy and array-comparative genomic hybridization between March 2011 and December 2016 in three laboratories. PARTICIPANTS/MATERIALS, SETTING, METHODS: The primary outcome measure was the number of EE on day-3. Statistical analysis was performed using the generalized estimating equations (GEE) framework and multivariate regression models to control for the clustered nature of the data while adjusting for potential confounders. MAIN RESULTS AND THE ROLE OF CHANCE: A multivariate regression GEE model including all significant population and stimulation characteristics as covariates as well as an interaction term between female age and number of oocytes revealed that the number of oocytes retrieved was still positively associated with the number of EE (coeff: +0.40, 95% CI: 0.24-0.56). The interaction term was highly significant (coeff: -0.01, P < 0.001) indicating an effect modifying role of female age on the association of oocytes retrieved with the number of EE. The number of oocytes retrieved was also positively associated with cumulative live birth rates (odds ratio: 1.07, 95% CI: 1.03-1.12). LIMITATIONS, REASONS FOR CAUTION: This study is retrospective and the presence of residual unknown bias cannot be excluded. Furthermore, the population analyzed in this study might not be completely representative of the general population undergoing ICSI. WIDER IMPLICATIONS OF THE FINDINGS: These results provide an explanatory mechanism for the recently published positive association between the number of oocytes retrieved and cumulative live birth rates. STUDY FUNDING/COMPETING INTEREST(S): CAV is supported by a NHMRC Early Career Fellowship (GNT1147154)/ No competing interests to declare.

What is the best predictor of severe ovarian hyperstimulation syndrome in IVF? A cohort study.

PURPOSE: The purpose of the present study is to study what is the best predictor of severe ovarian hyperstimulation syndrome (OHSS) in IVF. METHODS: This is a retrospective analysis of all consecutive IVF/intracytoplasmic injection cycles performed during a 5-year period (2009-2014) in a single university fertility centre. All fresh IVF cycles where ovarian stimulation was performed with gonadotrophins and GnRH agonists or antagonists and triggering of final oocyte maturation was induced with the administration of urinary or recombinant hCG were analyzed (2982 patients undergoing 5493 cycles). Because some patients contributed more than one cycle, the analysis of the data was performed with the use of generalized estimating equation (GEE). RESULTS: Severe OHSS was diagnosed in 20 cycles (0.36%, 95% CI 0.20-0.52). The number of follicles ≥10 mm on the day of triggering final oocyte maturation represents the best predictor of severe OHSS in IVF cycles. The cutoff in the number of follicles ≥10 mm with the best capacity to discriminate between women that will and will not develop severe OHSS was ≥15. CONCLUSION: The presence of more than 15 follicles ≥10 mm on the day of triggering final oocyte maturation represents the best predictor of severe OHSS in IVF cycles.

Blastocyst utilization rates after continuous culture in two commercial single-step media: a prospective randomized study with sibling oocytes.

PURPOSE: The aim of this study is to determine whether blastocyst utilization rates are different after continuous culture in two different commercial single-step media. METHODS: This is a paired randomized controlled trial with sibling oocytes conducted in infertility patients, aged ≤40 years with ≥10 oocytes retrieved assigned to blastocyst culture and transfer. Retrieved oocytes were randomly allocated to continuous culture in either Sage one-step medium (Origio) or Continuous Single Culture (CSC) medium (Irvine Scientific) without medium renewal up to day 5 post oocyte retrieval. Main outcome measure was the proportion of embryos suitable for clinical use (utilization rate). RESULTS: A total of 502 oocytes from 33 women were randomly allocated to continuous culture in either Sage one-step medium (n = 250) or CSC medium (n = 252). Fertilization was performed by either in vitro fertilization or intracytoplasmic sperm injection, and embryo transfers were performed on day 5. Two patients had all blastocysts frozen due to the occurrence of severe ovarian hyperstimulation syndrome. Fertilization and cleavage rates, as well as embryo quality on day 3, were similar in the two media. Blastocyst utilization rates (%, 95% CI) [55.4% (46.4-64.1) vs 54.7% (44.9-64.6), p = 0.717], blastocyst formation rates [53.6% (44.6-62.5) vs 51.9 (42.2-61.6), p = 0.755], and proportion of good quality blastocysts [36.8% (28.1-45.4) vs 36.1% (27.2-45.0), p = 0.850] were similar in Sage one-step and CSC media, respectively. CONCLUSIONS: Continuous culture of embryos in Sage one-step and CSC media is associated with similar blastocyst development and utilization rates. Both single-step media appear to provide adequate support during in vitro preimplantation embryo development. Whether these observations are also valid for other continuous single medium protocols remains to be determined. CLINICAL TRIAL REGISTRATION NUMBER: NCT02302638.