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.

A critical systematic review and meta-analyses of risk factors for fertility problems in a globalized world.

Globally, fertility awareness efforts include well-established risk factors for fertility problems. Risks disproportionately affecting women in the Global South, however, are neglected. To address this gap, we conducted a systematic review and meta-analyses of relevant risk factors to examine the association between risk factors and fertility problems. MEDLINE, Embase, Cochrane Library, regional databases and key organizational websites were used. Three authors screened and extracted data independently. Studies assessing exposure to risk (clinical, community-based samples) were included, and studies without control groups were excluded. Outcome of interest was fertility problems, e.g. inability to achieve pregnancy, live birth, neonatal death depending on study. The Newcastle-Ottawa Scale was used to assess study quality. A total of 3843 studies were identified, and 62 were included (58 in meta-analyses; n = 111,977). Results revealed the following: a ninefold risk of inability to become pregnant in genital tuberculosis (OR 8.91, 95% CI 1.89 to 42.12); an almost threefold risk in human immunodeficiency virus (OR 2.93, 95% CI 1.95 to 4.42) and bacterial vaginosis (OR 2.81, 95% CI 1.85 to 4.27); a twofold risk of tubal-factor infertility in female genital mutilation/cutting-Type II/III (OR 2.06, 95% CI 1.03 to 4.15); and postnatal mortality in consanguinity (stillbirth, OR 1.28, 95% CI 1.04 to 1.57; neonatal death, OR 1.57, 95% CI 1.22 to 2.02). It seems that risk factors affected reproductive processes through multiple pathways. Health promotion encompassing relevant health indicators could enhance prevention and early detection of fertility problems in the Global South and disproportionately affected populations. The multifactorial risk profile reinforces the need to place fertility within global health initiatives.

The role of endometrial scratching prior to in vitro fertilization: an updated systematic review and meta-analysis.

RESEARCH QUESTION: To evaluate the role of endometrial scratching performed prior to an embryo transfer cycle on the probability of pregnancy compared to placebo/sham or no intervention. DESIGN: A computerized literature (using a specific search strategy) search was performed across the databases MEDLINE, EMBASE, COCHRANE CENTRAL, SCOPUS and WEB OF SCIENCE up to June 2023 in order to identify randomized controlled trials (RCTs) evaluating the effect of endometrial scratching prior to an embryo transfer cycle on the probability of pregnancy, expressed either as live birth, ongoing pregnancy or clinical pregnancy (in order of significance) compared to placebo/sham or no intervention. Data were pooled using random-effects or fixed-effects model, depending on the presence or not of heterogeneity. Heterogeneity was assessed using the I2 statistic. Subgroup analyses were performed based on the population studied in each RCT, as well as on the timing and method of endometrial biopsy. Certainty of evidence was assessed using the GRADEPro tool. RESULTS: The probability of live birth was significantly higher in embryo transfer cycles after endometrial scratching as compared to placebo/sham or no intervention (relative risk-RR: 1.12, 95% CI: 1.05-1.20; heterogeneity: I2=46.30%, p<0.001, 28 studies; low certainty). The probability of ongoing pregnancy was not significantly difference between the two groups (RR: 1.07, 95% CI: 0.98-1.18; heterogeneity: I2=27.44%, p=0.15, 11 studies; low certainty). The probability of clinical pregnancy was significantly higher in embryo transfer cycles after endometrial scratching as compared to placebo/sham or no intervention (RR: 1.12, 95% CI: 1.06-1.18; heterogeneity: I2=47.48%, p<0.001, 37 studies; low certainty). A subgroup analysis was performed based on the time that endometrial scratching was carried out. When endometrial scratching was performed during the menstrual cycle prior to the embryo transfer cycle a significantly higher probability of live birth was present (RR: 1.18, 95% CI:1.09-1.27; heterogeneity: I2=39.72%, p<0.001, 21 studies; moderate certainty). On the contrary, no effect on the probability of live birth was present when endometrial injury was performed during the embryo transfer cycle (RR: 0.87, 95% CI: 0.67-1.15; heterogeneity: I2=65.18%, p=0.33, 5 studies; low certainty). In addition, a higher probability of live birth was only present in women with previous IVF failures (RR: 1.35, 95% CI: 1.20-1.53; heterogeneity: I2=0%, p<0.001, 13 studies; moderate certainty) with evidence suggesting that the more IVF failures the more likely endometrial scratching to be beneficial (p=0.004). The number of times endometrial scratching was performed, as well as the type of instrument used did not appear to affect the probability of live birth. CONCLUSIONS: Endometrial scratching during the menstrual cycle prior to an embryo transfer cycle can lead to a higher probability of live birth in patients with previous IVF failures. PROSPERO REGISTRATION: PROSPERO CRD42023433538 (18 Jun 2023).

Risk for Congenital Anomalies in Children Conceived With Medically Assisted Fertility Treatment : A Population-Based Cohort Study.

BACKGROUND: More than 2 million children are conceived annually using assisted reproductive technologies (ARTs), with a similar number conceived using ovulation induction and intrauterine insemination (OI/IUI). Previous studies suggest that ART-conceived children are at increased risk for congenital anomalies (CAs). However, the role of underlying infertility in this risk remains unclear, and ART clinical and laboratory practices have changed drastically over time, particularly there has been an increase in intracytoplasmic sperm injection (ICSI) and cryopreservation. OBJECTIVE: To investigate the role of underlying infertility and fertility treatment on CA risks in the first 2 years of life. DESIGN: Propensity score-weighted population-based cohort study. SETTING: New South Wales, Australia. PARTICIPANTS: 851 984 infants (828 099 singletons and 23 885 plural children) delivered between 2009 and 2017. MEASUREMENTS: Adjusted risk difference (aRD) in CAs of infants conceived through fertility treatment compared with 2 naturally conceived (NC) control groups-those with and without a parental history of infertility (NC-infertile and NC-fertile). RESULTS: The overall incidence of CAs was 459 per 10 000 singleton births and 757 per 10 000 plural births. Compared with NC-fertile singleton control infants (n = 747 018), ART-conceived singleton infants (n = 31 256) had an elevated risk for major genitourinary abnormalities (aRD, 19.0 cases per 10 000 births [95% CI, 2.3 to 35.6]); the risk remained unchanged (aRD, 22 cases per 10 000 births [CI, 4.6 to 39.4]) when compared with NC-infertile singleton control infants (n = 36 251) (that is, after accounting for parental infertility), indicating that ART remained an independent risk. After accounting for parental infertility, ICSI in couples without male infertility was associated with an increased risk for major genitourinary abnormalities (aRD, 47.8 cases per 10 000 singleton births [CI, 12.6 to 83.1]). There was some suggestion of increased risk for CAs after fresh embryo transfer, although estimates were imprecise and inconsistent. There were no increased risks for CAs among OI/IUI-conceived infants (n = 13 574). LIMITATIONS: This study measured the risk for CAs only in those children who were born at or after 20 weeks' gestation. Observational study design precludes causal inference. Many estimates were imprecise. CONCLUSION: Patients should be counseled on the small increased risk for genitourinary abnormalities after ART, particularly after ICSI, which should be avoided in couples without problems of male infertility. PRIMARY FUNDING SOURCE: Australian National Health and Medical Research Council.

Statins for women with polycystic ovary syndrome not actively trying to conceive.

BACKGROUND: Statins are lipid-lowering agents with pleiotropic actions. Experts have proposed that in addition to improving the dyslipidaemia associated with polycystic ovary syndrome (PCOS), statins may also exert other beneficial metabolic and endocrine effects, such as reducing testosterone levels. This is an update of a Cochrane Review first published in 2011. OBJECTIVES: To assess the efficacy and safety of statin therapy in women with PCOS who are not actively trying to conceive. SEARCH METHODS: We searched the Cochrane Gynaecology and Fertility Group specialised register, CENTRAL, MEDLINE, Embase, PsycINFO, CINAHLs, and four ongoing trials registers on 7 November 2022. We also handsearched relevant conference proceedings and the reference lists of relevant trials for any additional studies, and we contacted experts in the field for any further ongoing studies. SELECTION CRITERIA: We included randomised controlled trials (RCTs) that evaluated the effects of statin therapy in women with PCOS not actively trying to conceive. Eligible comparisons were statin versus placebo or no treatment, statin plus another agent versus the other agent alone, and statin versus another agent. We performed statistical analysis using Review Manager 5, and we assessed the certainty of the evidence using GRADE methods. DATA COLLECTION AND ANALYSIS: We used standard Cochrane methodology. Our primary outcomes were resumption of menstrual regularity and resumption of spontaneous ovulation. Our secondary outcomes were clinical and physiological measures including hirsutism, acne severity, testosterone levels, and adverse events. MAIN RESULTS: Six RCTs fulfilled the criteria for inclusion. They included 396 women with PCOS who received six weeks, three months, or six months of treatment; 374 women completed the studies. Three studies evaluated the effects of simvastatin and three studies evaluated the effects of atorvastatin. We summarised the results of the studies under the following comparisons. Statins versus placebo (3 RCTs) One trial measured resumption of menstrual regularity as menstrual cycle length in days. We are uncertain if statins compared with placebo shorten the mean length of the menstrual cycle (mean difference (MD) -2.00 days, 95% confidence interval (CI) -24.86 to 20.86; 37 participants; very low-certainty evidence). No studies reported resumption of spontaneous ovulation, improvement in hirsutism, or improvement in acne. We are uncertain if statins compared with placebo reduce testosterone levels after six weeks (MD 0.06, 95% CI -0.72 to 0.84; 1 RCT, 20 participants; very low-certainty evidence), after 3 months (MD -0.53, 95% CI -1.61 to 0.54; 2 RCTs, 64 participants; very low-certainty evidence), or after 6 months (MD 0.10, 95% CI -0.43 to 0.63; 1 RCT, 28 participants; very low-certainty evidence) Two studies recorded adverse events, and neither reported significant differences between the groups. Statins plus metformin versus metformin alone (1 RCT) The single RCT included in this comparison measured resumption of menstrual regularity as the number of spontaneous menses per six months. We are uncertain if statins plus metformin compared with metformin improves resumption of menstrual regularity (MD 0.60 menses, 95% CI 0.08 to 1.12; 69 participants; very low-certainty evidence). The study did not report resumption of spontaneous ovulation. We are uncertain if statins plus metformin compared with metformin alone improves hirsutism measured using the Ferriman-Gallwey score (MD -0.16, 95% CI -0.91 to 0.59; 69 participants; very low-certainty evidence), acne severity measured on a scale of 0 to 3 (MD -0.31, 95% CI -0.67 to 0.05; 69 participants; very low-certainty evidence), or testosterone levels (MD -0.03, 95% CI -0.37 to 0.31; 69 participants; very low-certainty evidence). The study reported that no significant adverse events occurred. Statins plus oral contraceptive pill versus oral contraceptive pill alone (1 RCT) The single RCT included in this comparison did not report resumption of menstrual regularity or spontaneous ovulation. We are uncertain if statins plus the oral contraceptive pill (OCP) improves hirsutism compared with OCP alone (MD -0.12, 95% CI -0.41 to 0.17; 48 participants; very low-certainty evidence). The study did not report improvement in acne severity. We are also uncertain if statins plus OCP compared with OCP alone reduces testosterone levels, because the certainty of the evidence was very low (MD -0.82, 95% CI -1.38 to -0.26; 48 participants). The study reported that no participants experienced significant side effects. Statins versus metformin (2 RCTs) We are uncertain if statins improve menstrual regularity compared with metformin (number of spontaneous menses per six months) compared to metformin (MD 0.50 menses, 95% CI -0.05 to 1.05; 1 RCT, 61 participants, very low-certainty evidence). No studies reported resumption of spontaneous ovulation. We are uncertain if statins compared with metformin reduce hirsutism measured using the Ferriman-Gallwey score (MD -0.26, 95% CI -0.97 to 0.45; 1 RCT, 61 participants; very low-certainty evidence), acne severity measured on a scale of 0 to 3 (MD -0.18, 95% CI -0.53 to 0.17; 1 RCT, 61 participants; very low-certainty evidence), or testosterone levels (MD -0.24, 95% CI -0.58 to 0.10; 1 RCT, 61 participants; very low-certainty evidence). Both trials reported that no significant adverse events had occurred. Statins versus oral contraceptive pill plus flutamide (1 RCT) According to the study report, no participants experienced any significant side effects. There were no available data for any other main outcomes. AUTHORS' CONCLUSIONS: The evidence for all main outcomes of this review was of very low certainty. Due to the limited evidence, we are uncertain if statins compared with placebo, or statins plus metformin compared with metformin alone, improve resumption of menstrual regularity. The trial evaluating statin plus OCP versus OCP alone reported neither of our primary outcomes. No other studies reported resumption of spontaneous ovulation. We are uncertain if statins improve hirsutism, acne severity, or testosterone. All trials that measured adverse events reported no significant differences between the groups.

Childbirth timing and completed family size by the mode of conception-the role of medically assisted reproduction: a population-based cohort study in Australia.

Background: With declining total fertility rates to below replacement levels amongst all high-, middle- and low-income countries, coupled with increasing use of medically assisted reproduction (MAR) treatments globally, we describe the impact of these treatments on completed family size and childbearing timing in a country with unlimited publicly funded access to MAR. Methods: We utilised a unique longitudinal propensity score-weighted population-based birth cohort that included nulliparous mothers who gave birth after all major forms of MAR treatments (assisted reproductive technologies [ART], ovulation induction [OI], and intrauterine insemination [IUI]) and after natural conception (reference category) in Australia, 2003-2017. We followed first-time mothers over their reproductive lifespan (15-50 years). The primary outcome was completed family size (i.e., the mean cumulative number of children per mother of our cohort) and the fertility gap (i.e., adjusted difference in completed family size between MAR conceptions and the reference). Findings: Our cohort includes 481,866 first-time mothers, mean follow-up of 13.8 years. ART mothers (n = 25,296) were six years older (mean age: 34.6 years) than mothers who conceived naturally (28.7 years (reference)) while OI/IUI mothers were only 2.2 years older (31.0 years) than the reference. ART mothers had up to 27% smaller completed family size (2.54 children) compared to OI/IUI mothers (2.98 children) and natural conception mothers (3.23 children). ART mothers who resided in the lower socioeconomic areas were less likely to reach a similar family size to the natural conception mothers (fertility gap of 0.83 fewer children per ART mother compared to natural conception mothers) than ART mothers who resided in the higher socioeconomic areas (0.43 fewer children). Interpretation: Greater awareness of the limitations of MAR treatment to resolve childlessness and achieve desired family size is needed. Furthermore, with policymakers increasingly turning to MAR treatment as a tool to reverse declining fertility rates, their potential impact should not be overestimated. Funding: Australian National Health and Medical Research Council.

Serum anti-müllerian hormone (AMH) concentration during pregnancy: a longitudinal study.

A prospective longitudinal cohort study aimed to longitudinally examine the kinetics of Anti-müllerian hormone (AMH) during the first two trimesters of pregnancy. Pregnant women with stored 1st trimester serum samples were recruited at 24-28 weeks gestation during their gestational diabetes testing, where they provided an additional serum sample. The samples were analysed for AMH, oestradiol and progesterone concentrations. A decrease in serum AMH was observed in 40 out of 45 (88.9%) (95% CI 75.9% to 96.3%) of the participants in this study. The median serum AMH concentration was 10.9 pmol/L in the 1st trimester and 6.5 pmol/L during the 2nd trimester, with a significantly different distribution of the values between the 1st and the 2nd trimester AMH samples (p<0.001). The median percentage of AMH difference of -39.8%. This study demonstrated a significant decrease in serum AMH levels from the 1st to the 2nd trimester of pregnancy. The absolute decrease in AMH levels seems to be positively associated with 1st trimester AMH levels, whereas the percentage of AMH difference is not. Further studies are required to elucidate the potential physiological mechanisms of this finding.

Freeze-all embryos during treatment with assisted reproduction: Health economic aspects.

Assisted reproductive technologies are evolving, with the most recent example being the introduction of the freeze-all policy during which a fresh embryo transfer does not take place and all embryos of good quality are cryopreserved to be used in future frozen embryo transfers. As the freeze-all policy is becoming more prevalent, it is important to review the economic aspects of this approach, along with considerations of efficacy and safety, and the role of emerging freeze-all-specific ovarian stimulation strategies. Based on the available evidence, the freeze-all policy presents distinct clinical advantages, particularly for high responders. Available health economic evaluations are limited. Two good-quality cost-effectiveness analyses based on randomized controlled trials suggest that the freeze-all strategy is unlikely to be cost-effective in non-polycystic ovarian syndrome (non-PCOS), normally responding patients. However, the cost-effectiveness of the freeze-all strategy in different populations of patients and in different settings has not been evaluated, nor has the clinical and economic efficacy of modern freeze-all-specific ovarian stimulation protocols that are likely to simplify treatment and make it more affordable for patients. Economic evaluations that incorporate good practice health technology assessment (HTA) methods are needed to compare freeze-all with conventional embryo transfer strategies. Furthermore, future research should address the unique limitation of traditional HTA methods in valuing a life conceived through fertility treatment.

Inter- and Intra-Observer Agreement Between Embryologists for Cytoplasmic String Assessment in Day 5/6 Human Blastocysts.

To investigate inter- and intra-observer agreement in the assessment of cytoplasmic string (CS) by embryologists on day 5/6 human blastocysts using the EmbryoViewer software. This was a prospective study involving five embryologists working between 2019 and 2020. Inter-observer agreement was calculated using assessments performed on 104 day 5/6 blastocysts regarding the presence, number, and location of CS and CS vesicle activity using timelapse videos. Intra-observer agreement was calculated when the same embryologists repeated the observations after a month's break. Inter- and intra-observer agreement was assessed using Fleiss' kappa coefficient and the intra-class correlation coefficient (ICC). The inter-observer agreement on the presence of CS (kappa: 0.477, 95% CI: 0.301-0.639) and their vesicles (kappa: 0.494, 95% CI: 0.345-0.643) was moderate, while the specific characteristics of CS assessment ranged from fair to moderate (kappa scores between: 0.157 and 0.563). The intra-observer agreement indicated an improvement on the level of agreement (kappa scores between: 0.162 and 0.795) compared to the inter-observer agreement. This study has shown a moderate level of inter- and intra-observer agreement when assessing day 5/6 human blastocysts for the presence of CS and their vesicles. When the specific characteristics of CS assessment occurred (such as the number of CS/vesicles) a slight to moderate level of agreement was seen among the embryologists. Agreement of specific characteristics of CS was not optimal, suggesting the need for further training using specifically designed CS quality assurance programme (QAP) modules, to determine if inter- and intra-observer agreement can be improved.

Detailed analysis of cytoplasmic strings in human blastocysts: new insights.

The aim of this study was to determine if there was an association between the presence of cytoplasmic strings (CS) and their characteristics, with blastocyst quality, development and clinical outcome in human blastocysts. This two-centre cohort study was performed between July 2017 and September 2018 and involved a total of 1152 blastocysts from 225 patients undergoing in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). All embryos were cultured in Embryoscope+ and were assessed for CS using time-lapse images. A single assessor examined all blastocysts and reviewed videos using the EmbyroViewer® Software. Blastocyst quality was assessed on day 5 of embryo development. The number of CS, location and duration of their activity was recorded on days 5/6. A positive association between the presence of CS in human blastocysts with blastocyst quality was identified. Blastocysts with a higher number of CS present, were of higher quality and were in the more advanced stages of development. Top quality blastocysts had CS activity present for longer, as well as having a higher number of vesicles present travelling along the CS. Blastocysts that had CS present, had a significantly higher live birth rate. This study has confirmed that a higher number of CS and vesicles in human blastocysts is associated with top quality blastocysts and is not a negative predictor of development. They had a higher number of CS present that appeared earlier in development and, although ceased activity sooner, had a longer duration of activity. Blastocysts with CS had a significant increase in live birth rate.

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.

Is there an optimal window of time for transferring single frozen-thawed euploid blastocysts? A cohort study of 1170 embryo transfers.

STUDY QUESTION: Is there an optimal window of time when the transfer of single frozen-thawed euploid blastocysts is associated with a maximal live birth rate (LBR)? SUMMARY ANSWER: Performing a single frozen-thawed euploid blastocyst transfer at 160 ± 4 h post-hCG trigger in modified-natural frozen-thawed embryo transfer (FET) cycles was independently associated with a higher LBR as compared to transfers outside this window; however, in natural FET cycles, LBRs were comparable across a wider range of time intervals. WHAT IS KNOWN ALREADY: There is compelling evidence for maintaining embryo-endometrial synchrony to optimize clinical outcomes following FETs, which could potentially be achieved by matching the transfer time of an embryo post-ovulation to its developmental age post-oocyte retrieval. For modified-natural cycles, ovulation is widely accepted to occur ∼40 h following the hCG trigger, whilst ovulation following spontaneous LH surge onset is thought to vary from 24 to 56 h. STUDY DESIGN, SIZE, DURATION: This is a multicentered retrospective cohort study analyzing 1170 single frozen-thawed euploid blastocyst transfers following trophectoderm biopsy and preimplantation genetic testing (PGT) between May 2015 and February 2019. Limiting the analysis to single euploid embryo transfers allowed for a more accurate estimation of the endometrial synchrony factor by controlling for the developmental stage of the embryo (full blastocyst or more advanced) and its genetic composition. LBR per FET was the primary outcome measure. PARTICIPANTS/MATERIALS, SETTING, METHODS: Patients underwent natural or gonadotrophin-induced preparation of the endometrium, with serial serum oestradiol, LH and progesterone measurements. Optimally timed transfers were predefined as those conducted 120 ± 4 h post-ovulation since biopsy and subsequent cryopreservation of full blastocysts which is usually performed at 116-124 h post-oocyte retrieval. This was considered the equivalent of 160 ± 4 h post-hCG trigger in modified-natural cycles (n = 253), as ovulation was assumed to occur ∼40 h after the hCG trigger. For natural cycles (n = 917), this was also considered to be, on average, 160 ± 4 h post the spontaneous LH surge. Thus, study groups were determined as those with optimal timing or not, and additional exploratory and subgroup analyses were performed, varying the time window in terms of onset and width, both overall and per endometrial preparation protocol. Statistical analysis was performed using the generalized estimating equations (GEE) framework to control for the clustered nature of the data while adjusting for potential confounders. MAIN RESULTS AND THE ROLE OF CHANCE: Overall, LBRs were significantly higher when the transfer had been performed at 160 ± 4 h post-hCG trigger or LH surge onset compared to when it had been performed outside this window (44.7% vs 36.0%; P = 0.008). A multivariable regression GEE model including the cycle type (natural versus modified-natural), previtrification embryo quality (top versus good quality), embryo stage (fully hatched versus hatching or earlier blastocyst), vitrification day (D5 versus D6) and survival rate (>90% versus <90%) as covariates, confirmed that, overall, embryo transfers conducted 160 ± 4 h post-hCG trigger or LH surge onset (the assumed equivalent of 120 ± 4 h post-ovulation) were associated with a significantly higher LBR (relative risk (RR) 1.21, 95% CI 1.04-1.41). Subgroup exploratory analyses per endometrial preparation protocol demonstrated that these findings were primarily present in the modified-natural cycle group (RR 1.52, 95% CI 1.15-1.99), whilst the natural cycle group showed comparable LBRs across a wider range of time intervals. Moreover, the overall LBR for the natural group (36.8%; 95% CI 33.7-39.9%) was lower than that of the modified-natural group (41.3%; 95% CI 35.4-47.1%), suggesting that there likely remains a greater potential to further optimize the timing of natural cycle embryo transfers. LIMITATIONS, REASONS FOR CAUTION: As with all retrospective studies, the presence of residual unknown bias cannot be excluded. Additionally, patients included in this study were a selected group who underwent PGT for specific reasons and hence the results obtained might not be directly applicable to the general population or embryos that have not undergone embryo biopsy. Furthermore, the criteria utilized to interpret hormonal data from natural cycles were specifically adopted for the present study and need to be validated in further studies. WIDER IMPLICATIONS OF THE FINDINGS: The results of this study highlight the significance of embryo-endometrial synchrony for the optimization of frozen embryo transfer outcome. However, it also clearly supports that the implantation window is in most cases wide and the achievement of live birth is possible with relatively high success rates even outside the optimal window of 160 ± 4 h post-trigger for modified-natural cycles and across a range of time intervals for natural cycles. Additionally, this study suggests that implantation rates could be further optimized in natural cycles by improving methods of assessing embryo-endometrial synchrony. STUDY FUNDING/COMPETING INTEREST(S): C. V. is supported by a National Health and Medical Research Council Early Career Fellowship (GNT1147154). No other funding was received for this study and there are no competing interests. TRIAL REGISTRATION NUMBER: N/A.

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.

Originator recombinant human follitropin alfa versus recombinant human follitropin alfa biosimilars in Spain: A cost-effectiveness analysis of assisted reproductive technology related to fresh embryo transfers.

This study compared the cost per live birth and cost-effectiveness of the originator recombinant human follicle-stimulating hormone follitropin alfa (r-hFSH-alfa) and r-hFSH-alfa biosimilars for ovarian stimulation prior to assisted reproductive technology treatment in Spain. A decision tree model was developed, comprising pregnancy and live birth for one treatment cycle with fresh embryo transfer. Clinical inputs were based on a recent meta-analysis by Chua et al. [4]. Cost inputs were extracted from publicly available Spanish sources. The costs per live birth were lower with originator r-hFSH-alfa (€18,138) versus r-hFSH-alfa biosimilars (€20,377). The incremental cost-effectiveness ratio was €7208 for originator r-hFSH-alfa versus biosimilars. Drug acquisition costs for originator r-hFSH-alfa represented 10.5% of total costs in the base case analysis, and 6.2% in a treatment cycle resulting in live birth with one fresh embryo transfer. Results from the sensitivity analyses confirmed the robustness of the findings.

Population-wide contribution of medically assisted reproductive technologies to overall births in Australia: temporal trends and parental characteristics.

STUDY QUESTION: In a country with supportive funding for medically assisted reproduction (MAR) technologies, what is the proportion of MAR births over-time? SUMMARY ANSWER: In 2017, 6.7% of births were conceived by MAR (4.8% ART and 1.9% ovulation induction (OI)/IUI) with a 55% increase in ART births and a stable contribution from OI/IUI births over the past decade. WHAT IS KNOWN ALREADY: There is considerable global variation in utilization rates of ART despite a similar infertility prevalence worldwide. While the overall contribution of ART to national births is known in many countries because of ART registries, very little is known about the contribution of OI/IUI treatment or the socio-demographic characteristics of the parents. Australia provides supportive public funding for all forms of MAR with no restrictions based on male or female age, and thus provides a unique setting to investigate the contribution of MAR to national births as well as the socio-demographic characteristics of parents across the different types of MAR births. STUDY DESIGN, SIZE, DURATION: This is a novel population-based birth cohort study of 898 084 births using linked ART registry data and administrative data including birth registrations, medical services, pharmaceuticals, hospital admissions and deaths. Birth (a live or still birth of at least one baby of ≥400 g birthweight or ≥20 weeks' gestation) was the unit of analysis in this study. Multiple births were considered as one birth in our analysis. PARTICIPANTS/MATERIALS, SETTING, METHODS: This study included a total of 898 084 births (606 488 mothers) in New South Wales and the Australian Capital Territory, Australia 2009-2017. We calculated the prevalence of all categories of MAR-conceived births over the study period. Generalized estimating equations were used to examine the association between parental characteristics (parent's age, parity, socio-economic status, maternal country of birth, remoteness of mother's dwelling, pre-existing medical conditions, smoking, etc.) and ART and OI/IUI births relative to naturally conceived births. MAIN RESULTS AND THE ROLE OF CHANCE: The proportion of MAR births increased from 5.1% of all births in 2009 to 6.7% in 2017, representing a 30% increase over the decade. The proportion of OI/IUI births remained stable at around 2% of all births, representing 32% of all MAR births. Over the study period, ART births conceived by frozen embryo-transfer increased nearly 3-fold. OI/IUI births conceived using clomiphene citrate decreased by 39%, while OI/IUI births conceived using letrozole increased 56-fold. Overall, there was a 55% increase over the study period in the number of ART-conceived births, rising to 56% of births to mothers aged 40 years and older. In 2017, almost one in six births (17.6%) to mothers aged 40 years and over were conceived using ART treatment. Conversely, the proportion of OI/IUI births was similar across different mother's age groups and remained stable over the study period. ART children, but not OI/IUI children, were more likely to have parents who were socio-economically advantaged compared to naturally conceived children. For example, compared to naturally conceived births, ART births were 16% less likely to be born to mothers who live in the disadvantaged neighbourhoods after accounting for other covariates (adjusted relative risk (aRR): 0.84 [95% CI: 0.81-0.88]). ART- or OI/IUI-conceived children were 25% less likely to be born to immigrant mothers than births after natural conception (aRR: 0.75 [0.74-0.77]). LIMITATIONS, REASONS FOR CAUTION: The social inequalities that we observed between the parents of children born using ART and naturally conceived children may not directly reflect disparities in accessing fertility care for individuals seeking treatment. WIDER IMPLICATIONS OF THE FINDINGS: With the ubiquitous decline in fertility rates around the world and the increasing trend to delay childbearing, this population-based study enhances our understanding of the contribution of different types of MARs to population profiles among births in high-income countries. The parental socio-demographic characteristics of MAR-conceived children differ significantly from naturally conceived children and this highlights the importance of accounting for such differences in studies investigating the health and development of MAR-conceived children. STUDY FUNDING/COMPETING INTEREST(S): This study was funded through Australian National Health and Medical Research Council (NHMRC) grant: APP1127437. G.M.C. is an employee of The University of New South Wales (UNSW) and Director of the National Perinatal Epidemiology and Statistics Unit (NPESU), UNSW. The NPESU manages the Australian and New Zealand Assisted Reproduction Database with funding support from the Fertility Society of Australia and New Zealand. C.V. is an employee of The University of New South Wales (UNSW), Director of Clinical Research of IVFAustralia, Member of the Board of the Fertility Society of Australia and New Zealand, and Member of Research Committee of School of Women's and Children's Health, UNSW. C.V. reports grants from Australian National Health and Medical Research Council (NHMRC), and Merck KGaA. C.V. reports consulting fees, and payment or honoraria for lectures, presentations, speakers, bureaus, manuscript, writing or educational events or attending meeting or travel from Merck, Merck Sparpe & Dohme, Ferring, Gedon-Richter and Besins outside this submitted work. C.V. reported stock or stock options from Virtus Health Limited outside this submitted work. R.J.N. is an employee of The University of Adelaide, and Chair DSMC for natural therapies trial of The University of Hong Kong. R.J.N. reports grants from NHMRC. R.J.N. reports lecture fees and support for attending or travelling for lecture from Merck Serono which is outside this submitted work. L.R.J. is an employee of The UNSW and Foundation Director of the Centre for Big Data Research in Health at UNSW Sydney. L.R.J. reports grants from NHMRC. The other co-authors have no conflict of interest. TRIAL REGISTRATION NUMBER: N/A.

A bespoke data linkage of an IVF clinical quality registry to population health datasets; methods and performance.

INTRODUCTION: Assisted reproductive technologies (ART), such as in-vitro fertilisation (IVF), have revolutionised the treatment of infertility, with an estimated 8 million babies born worldwide. However, the long-term health outcomes for women and their offspring remain an area of concern. Linking IVF treatment data to long-term health data is the most efficient method for assessing such outcomes. OBJECTIVES: To describe the creation and performance of a bespoke population-based data linkage of an ART clinical quality registry to state-based and national administrative datasets. METHODS: The linked dataset was created by deterministically and probabilistically linking the Australia and New Zealand Assisted Reproduction Database (ANZARD) to New South Wales (NSW) and Australian Capital Territory (ACT) administrative datasets (performed by NSW Centre for Health Record Linkage (CHeReL)) and to national claims datasets (performed by Australian Institute of Health and Welfare (AIHW)). The CHeReL's Master Linkage Key (MLK) was used as a bridge between ANZARD's partially identifiable patient data (statistical linkage key) and NSW and ACT administrative datasets. CHeReL then provided personal identifiers to the AIHW to obtain national content data. The results of the linkage were reported, and concordance between births recorded in ANZARD and perinatal data collections (PDCs) was evaluated. RESULTS: Of the 62,833 women who had ART treatment in NSW or ACT, 60,419 could be linked to the CHeReL MLK (linkage rate: 96.2%). A reconciliation of ANZARD-recorded births among NSW residents found that 94.2% (95% CI: 93.9-94.4%) of births were also recorded in state/territory-based PDCs. A high concordance was found in plurality status and birth outcome ≥99% agreement rate, Cohen's kappa ranged: 0.78-0.98) between ANZARD and PDCs. CONCLUSION: The data linkage resource demonstrates that high linkage rates can be achieved with partially identifiable data and that a population spine, such as the CHeReL's MLK, can be successfully used as a bridge between clinical registries and administrative datasets.

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.