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Women with polycystic ovary syndrome make up the vast majority of patients with anovulatory infertility. The commonly accepted treatment guidelines recommend ovulation induction for timed intercourse as the first-line treatment. After a 2-year treatment period, the cumulative pregnancy rates with a singleton live-born baby reached 71% and 78% in two prospective studies. Despite aiming for monofollicular growth, multifollicular responses with subsequent multiple/higher order multiple pregnancies are a dreaded risk associated with ovarian induction. However, the lengthy treatment, the increase of maternal age and the psychological effects of 'obligatory intercourse' are also factors challenging the concept of ovarian induction as the first treatment approach in anovulatory infertility. Nowadays, individualized IVF treatment with cycle segmentation, freeze-all strategies and single-embryo transfers in frozen embryo transfer cycles dramatically reduces the risk of multiple pregnancies, and a cumulative pregnancy rate of 83% can be achieved over three complete cycles, thereby reducing exposure to fertility medication and time to pregnancy. Although on first sight ovarian induction might present the easier and less costly approach, efficient and individualized IVF treatments with low complication rates and the chance of preventing multiple pregnancies challenge this concept, and it seems that the time has come to abandon ovarian induction in anovulatory infertility.

Is there a difference in the blood flow of the Arteria uterina in frozen embryo transfer (FET) cycles between a Natural Cycle (NC) and a Hormonal Replacement Therapy (HRT) cycle?Prospective observational study with measurement of the pulsatility index (PI) and resistance index (RI) throughout the ovarian stimulation cycle for IVF/ICSI, the FET cycle and at 12 weeks of gestation.A total of 124 ovarian stimulation cycles with preimplantation genetic testing for aneuploidy (PGT-A) and "freeze-all" strategy due to PGT-A were included. Mean patient's age was 31.4 years, mean BMI 26.47 kg/m2, mean AMH 3.62 ng/ml and a mean AFC of 13. FET cycles were performed in 77 patients (NC protocol: 37.7%, HRT protocol: 62.2%). The overall pregnancy rate was 75%, (NC group: 79%, HRT-group 73%; not significant). No significant change of PI and RI was seen during hormonal stimulation. In FET cycles, there was a significant increase between cycle day 2/3 and ovulation/P4-start in the HRT-cycle, followed by a significant decrease until 12 weeks of gestation. The slope of the decrease in patients with a pregnancy in an HRT-approach was a bit steeper than in the NC-approach for both PI and RI, however, without a significant difference.Early measurements of the blood flow parameters during the FET cycle do not reveal a difference between the NC- and the HRT-approach for FET, which could be predictive for development of pre-eclampsia.

OBJECTIVE: To determine which variables affect most the clinical pregnancy rate with positive fetal heartbeat (CPR FHB+) when frozen embryo transfer (FET) cycles are performed with day 5 (D5) or day 6 (D6) euploid blastocysts. Design and method A single center retrospective study was performed from March 2017 till February 2021 including all single FET cycles with euploid D5 or D6 blastocysts and transferred in natural cycles (NC) or hormone replacement therapy (HRT) cycles. Trophectoderm (TE) and inner cell mass (ICM) qualities were recorded before biopsy. RESULTS: A total of 1102 FET cycles were included, 678 with D5 and 424 with D6 blastocysts. Pregnancy rate (PR), clinical PR (CPR), and CPR FHB+ were significantly higher with D5 blastocysts (PR: 70.7% vs 62.0%, OR = 0.68 [0.53–0.89], p = 0.004; CPR: 63.7% vs 54.2%, OR = 0.68 [0.52–0.96], p = 0.002 and CPR FHB+: 57.8% vs 49.8%, OR = 0.72 [0.53–0.96], p = 0.011). However, miscarriage rate (12.5% vs 11.4%, OR = 0.78 [0.48–1.26], p = 0.311) did not differ. From a multivariate logistic regression model, endometrial thickness (OR = 1.11 [1.01–1.22], p = 0.028), patient’s age (OR = 1.03 [1.00–1.05], p = 0.021), BMI (OR = 0.97 [0.94–0.99], p = 0.023), and ICM grade C (OR = 0.23 [0.13–0.43], p < 0.001) were significant in predicting CPR FHB+. CONCLUSION: Although clinical outcomes are higher with D5 blastocysts, CPR FHB+ is more affected by endometrial thickness, patient age, BMI, and ICM grade C rather than biopsy day or endometrial preparation protocol. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10815-021-02380-1.

To evaluate the impact of a cesarean section (CS) on the chance of clinical pregnancy and live birth (LB) in frozen embryo transfer (FET) cycles in the setting of euploid embryos and the absence of intracavitary fluid (ICF) as causes of implantation failure were excluded.Retrospective study, including patients with at least one previous CS or at least one previous vaginal delivery, who underwent a euploid FET cycle.A total of 412 euploid embryo transfer cycles had been included. Patients' mean age was 34.5 years and 42.48% of patients have had at least one previous CS. A clinical pregnancy was seen in 69.42% and 60.19% of the patients had a LB. Positive pregnancy test, clinical pregnancy, and LB rate were not significantly different between the groups without/with a history of a previous CS (p = 0.6/0.45/0.94, respectively). LB rate was significantly reduced by the presence of mucus on the ET catheter (OR: 0.413; p = 0.010), the BMI (OR: 0.946; p = 0.006), the combined embryo quality (embryo quality fair: OR: 0.444; p = 0.001; embryo quality low: OR: 0.062; p 0.001), and by the HRT endometrial preparation approach (OR: 0.609; p = 0.023).The possible negative impact of a CS can be overcome when a euploid FET after exclusion of ICF is performed.

PURPOSE: To determine if euploidy rates and embryo development differ when blastocysts are cultured in CCM or SCM. METHOD: A single-center retrospective observational study was performed from September 2018 to March 2019. Patients [23–46 years] with at least four fresh mature oocytes (MII) without severe male factor infertility were included. Sibling MII were injected and cultured in Global®Total®LP (CCM) or Sage Quinn’s Advantage® Cleavage and Blastocyst media (SCM) under 6% CO(2), 5% O(2), and 89% N(2). Fertilization, cleavage, day (D) 5 blastulation, usable blastocyst (blastocysts biopsied/normally fertilized oocytes), and euploidy rates were recorded. Blastocysts were graded prior to trophectoderm (TE) biopsy on D5, 6, or 7 for genetic testing and mitochondrial DNA (mtDNA) quantification. RESULTS: According to clinical practice, 1452 MII were randomly distributed: 751 in CCM and 701 in SCM. No differences were observed in fertilization and cleavages rates for CCM and SCM (77.4% vs 75.5%, p = 0.429 and 97.6% vs 99.1%, p = 0.094, respectively). Blastulation rate on D5 was higher in CCM (70.6% vs 62.2, p = 0.009); however, usable blastocyst rates were comparable (CCM: 58.3% vs SCM: 56.7%, p = 0.625). From a Poisson regression model adjusted for confounding factors, euploidy rates were not different between media (aOR = 1.18, [0.94–1.48], p = 0.157). Euploid blastocyst’s mtDNA values were similar (CCM: 32.2, [30.5, 34.1] and SCM: 33.5, [31.8, 35.2], p = 0.345) and top-quality blastocysts (AA/BA) were increased in SCM (OR=1.04, [1.00–1.09], p = 0.037). CONCLUSION: Under controlled in vitro conditions, euploidy rates and embryo development are comparable when embryos are cultured in CCM or SCM. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10815-021-02187-0.

PURPOSE: To determine whether the blastocyst mitochondrial DNA (mtDNA) content is related to the miscarriage rate in patients undergoing single euploid frozen embryo transfer (SEFET). METHODS: A total of 355 single euploid frozen embryo transfer cycles were studied retrospectively between April 2017 and December 2018. A trophectoderm biopsy was performed on day 5/6 blastocysts. Post next-generation sequencing (NGS), the mtDNA content was calculated as the ratio of mitochondrial DNA over nuclear DNA, and the association between blastocyst mtDNA content and miscarriage rate was evaluated. RESULT(S): Three hundred fifty-five euploid blastocysts were selected for SEFET in 314 patients with an average age of 33.7 ± 5.6 years; 255 were biopsied on day 5 (71.8%) and 100 on day 6 (28.2%). Frozen embryo transfer (FET) was performed either in a hormone replacement therapy (HRT) cycle (71.8%; n = 255) or in a natural cycle (NC) (28.2%; n = 100). A pregnancy rate of 66.2% (235/355) was obtained with clinical pregnancy and miscarriage rates of 52.4% (n = 186) and 5.6% (n = 20), respectively. There was no significant difference neither between the blastocyst mtDNA content of pregnant and nonpregnant patients (27.7 ± 9.2 vs. 29.4 ± 8.6, P = 0.095) nor between patients with a clinical pregnancy and miscarriage (30.5 ± 9.3 vs. 27.3 ± 9.2, P = 0.136). Multivariate logistic regression analysis showed the same nonsignificant relationship, except for the miscarriage rate and BMI (OR 1.149, 95% CI 1.03–1.28; P = 0.012). CONCLUSION(S): Mitochondrial DNA content is unable to predict the miscarriage of implanted human euploid blastocysts. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10815-020-02050-8.

PURPOSE: To evaluate whether mtDNA content at the blastocyst stage differs between embryos derived from fresh or vitrified sibling oocytes. MATERIAL AND METHODS: A retrospective analysis was performed between March 2017 and September 2018, including 504 blastocysts from 94 couples undergoing preimplantation genetic testing for aneuploidies (PGT-A), using fresh oocytes together with previously vitrified oocytes. Trophectoderm biopsies were performed and subjected to next generation sequencing. RESULTS: On average, 1.8 ± 1.0 oocyte vitrification cycles were performed per patient. Between fresh and vitrified cycles, no difference was observed between the number of fertilized oocytes (5.3 ± 4.2 versus 5.5 ± 3.0). Blastulation rate on day 5 per fertilized oocyte was significantly higher in the fresh group (62% ± 29% versus 44% ± 31%; p

The implementation of cryopreservation-techniques in the IVF laboratory and the improved survival rates of oocytes, cleavage and blastocyst stage embryos have led to a significant increase in the number of frozen-thawed embryo transfer cycles (FET). FETs can be planned either in a 'pure' natural cycle, a modified natural cycle, a stimulated cycle or a hormonal replacement therapy cycle and the optimal means to prepare the endometrium for frozen embryo transfer is a topic of ongoing controversy. Recent findings report an increased risk of hypertensive disorders if pregnancy is achieved in a frozen embryo transfer cycle without an existing corpus luteum. Therefore, the question of how to prepare the endometrium has gained even more importance and taken on a new dimension as it should not simply be reduced to the basic question of 'which approach will result in superior pregnancy rates?' but instead 'which approach will result in the best pregnancy rates and the safest outcome for mother and baby?'. The aim of this review is to summarize and critically appraise the existing data on the different approaches of endometrial preparation for frozen embryo transfer with a special focus on the 'pure' natural cycle.

STUDY QUESTION What is the risk of developing intracavitary fluid (ICF) during ovarian stimulation in patients with an isthmocele after previous caesarean section (CS) delivery? SUMMARY ANSWER In patients with an existing isthmocele, the risk of developing ICF during hormonal stimulation for IVF is almost 40%; therefore, special attention has to be paid to exclude fluid accumulation during stimulation and particularly at the time of transfer, in which case the reproductive outcomes of frozen embryo transfer (FET) cycles appear to be uncompromised. WHAT IS KNOWN ALREADY Lately, there is an increasing focus on the long-term impact of CS delivery on the health and future fertility of the mother. Development of an isthmocele is one of the sequelae of a CS delivery. The presence of ICF in combination with an isthmocele has been described previously, and the adverse effect of endometrial fluid on implantation is well recognised by reproductive medicine specialists. Accumulation of ICF has been previously described in patients with hydrosalpinx, less commonly in patients with polycystic ovary syndrome undergoing ovarian stimulation for IVF/ICSI, and even in some patients without any identifiable reason. Assisted reproductive techniques (ARTs) are a means to overcome infertility. Reproductive medicine specialists commonly see patients with secondary infertility with a history of having had one or more previous CS and with ultrasound confirmation of an isthmocele. However, the available data pertaining to the prevalence of intracavitary fluid during ovarian stimulation in patients with ultrasound confirmation of an isthmocele is limited. Furthermore, data on the influence of ICF in a stimulated cycle on the ART outcome of a subsequent FET cycle is scarce and merits further studies. STUDY DESIGN, SIZE, DURATION A prospective observational exploratory study was performed in IVI Middle East Fertility Clinic, Abu Dhabi, from June 2018 to March 2019, and retrospective analysis of the reproductive outcomes was performed until July 2019. PARTICIPANTS/MATERIALS, SETTING, METHODS Patients with secondary infertility, defined as a minimum of 1 year of infertility after a previous successful pregnancy, undergoing ovarian stimulation for IVF/ICSI and having a history of one or more previous CS with ultrasonographic visible isthmocele, were included (n = 103). Patients were monitored as a clinical routine with vaginal ultrasound examinations during ovarian stimulation for IVF/ICSI treatment. All patients included in the study were asked to complete a questionnaire regarding their previous obstetric history. Development of ICF was recorded as well as changes in the measurements of the isthmocele during the course of ovarian stimulation. Reproductive outcomes of FET cycles of the patients with an isthmocele were retrospectively compared to those of patients with infertility and without isthmocele in our clinic during the same time period. MAIN RESULTS AND THE ROLE OF CHANCE Patients with an existing isthmocele after previous CS have a risk of ~40% of developing ultrasonographic visible fluid in the endometrial cavity during the course of ovarian stimulation. Development of ICF was significantly correlated with the depth of the isthmocele on Day 2/3 (P = 0.038) and on the day of trigger (−1/−2 days) (P = 0.049), circumference of the isthmocele on the day of trigger (−1/−2 days) (P = 0.040), distance from the C-scar to the external os (P = 0.036), number of children delivered (P = 0.047) and number of previous CS (P = 0.035). There was a statistically significant increase in the parameters related to the size of the isthmocele during ovarian stimulation. No significant differences in the reproductive outcome (pregnancy rate and rates of biochemical and ectopic pregnancies, miscarriages and ongoing/delivered pregnancies) after FET were found between the patients with and without an isthmocele, when ICF was excluded prior to embryo transfer procedure. LARGE-SCALE DATA NA. LIMITATIONS, REASONS FOR CAUTION This study was not primarily designed to investigate the causes of ICF during ovarian stimulation or to evaluate the reproductive outcomes. Further, the small number of reported reproductive outcomes may be seen as a limitation. WIDER IMPLICATIONS OF THE FINDINGS The data highlights the need for an increased awareness on the part of reproductive medicine specialists towards the potentially adverse impact of an isthmocele on ART treatment, as there is a potential to develop intracavitary fluid during ovarian stimulation for IVF. The increase in the circumference of the isthmocele may increase embryo transfer difficulty. STUDY FUNDING/COMPETING INTEREST(S) No funding of the study has to be reported. The authors have no competing interests. TRIAL REGISTRATION NUMBER This prospective study was registered with clinicaltrials.gov. under the number NCT03518385.

What is the impact of systemic FSH concentrations during ovarian stimulation for IVF/intracytoplasmic sperm injection on systemic progesterone concentrations in the late follicular phase?Post-hoc analysis of a previously performed randomized controlled trial (RCT) performed between November 2017 and February 2020 in a tertiary IVF centre. The RCT included patients with infertility undergoing ovarian stimulation in a gonadotrophin-releasing hormone (GnRH) antagonist protocol. The GnRH antagonist was administered at 08:00 h and recombinant FSH at 20:00 h. Ultrasound and blood tests were performed 3-5 h after the GnRH antagonist.The subgroup analysis comprised 105 patients. Systemic FSH concentrations increased from Day 2/3 until initiation of GnRH antagonist and remained constant until the day of trigger (DoT). The total group was split according to the median FSH DoT concentration (12.95 IU/l; Group A12.95 IU/l; Group B ≥12.95 IU/l). Significant differences, with the higher concentrations in Group B, were found for: systemic FSH concentration on Day 2/3 (P = 0.04), total gonadotrophin dosage (P = 0.03), progesterone on DoT (P = 0.001) and progesterone per follicle (P = 0.004). In the total group, systemic DoT FSH concentration was statistically significantly positively correlated with the DoT progesterone concentration and the ratio of progesterone per follicle (ρ = 0.37 and 0.38, respectively, both P 0.001). No significant correlations were seen between the systemic DoT FSH concentration and the number of retrieved oocytes.While ovarian response seems to be independent from the systemic FSH concentrations on the DoT, high concentrations of circulatory FSH augment the production of progesterone.

Is parental consanguinity associated with a reduced ovarian reserve in women from the Arabian Peninsula, comparing anti-Müllerian hormone (AMH) and antral follicle count (AFC)?Retrospective large-scale observational study including 2482 women from the Arabian Peninsula, aged 19-49 years, who had their serum AMH and AFC measured as part of their fertility assessment, from May 2015 to November 2019. Consanguinity was defined as women whose parents were first-degree or second-degree cousins. Serum AMH was measured for all participants.A total of 2198 women were included: 605 in the consanguine group (27.53%), 1593 (72.47%) in the non-consanguine group. There were no significant differences between groups in terms of body mass index, years of infertility or smoking status. Women from the consanguine group were significantly younger (mean age 33.74 ± 6.64 years) compared with the non-consanguine group (mean age 34.78 ± 6.64 years, P 0.0001). Median AMH and AFC for the consanguine group were 1.90 ng/ml (min-max: 0.01-23.8) and 11 (0-80), respectively, and for the non-consanguine group 1.84 ng/ml (min-max: 0.01-23.0) and 11 (0-60), respectively. AMH and AFC exhibit an age-dependent decline. As both parameters are age-dependent, the multivariate analysis showed that women from the consanguine group presented significantly lower AMH (coefficient of variation [CV] -0.07 ± 0.03, P = 0.036) and AFC (CV -0.16 ± 0.06, P = 0.003) compared with non-consanguine women, and the highest differences were found for women below 35 years of age (AMH median [min-max]: 2.82 ng/ml (0.01-23.80) versus 2.92 ng/ml (0.01-23.00); P = 0.035; AFC median [min-max]: 15 (0-80) versus 14 (0-80); P = 0.001).The adjusted analysis by age indicates that female parental consanguinity is associated with reduced ovarian reserve in the studied population. Clinical evaluation should include extensive family history and subsequent counselling of the affected couples.

Study question Does the limited exposure of embryos outside the incubator, during evaluation and changeover, have an impact on the blastocyst development, blastocyst quality and euploid outcomes? Summary answer Exposure of embryos outside the incubator, negatively impacts the number, quality and euploidy rate of day 5 blastocysts. What is known already The laboratory environment with its culture conditions is one of the crucial elements of the delicate equation to a successful ART outcome. It has been shown that increased fluctuations in the culture conditions have a considerable impact on the number of blastocysts obtained and cycle outcomes. Compared to conventional benchtop incubators, Time Lapse Technology (TLT) incubators capture images of the embryo and allow morphologic and morphokinetic assessment without disturbance during incubation. Several studies have been published comparing the efficiency, safety and outcome performance between conventional and TLT incubators, however, none of them explored the euploid outcomes. Study design, size, duration An observational sibling oocyte study was performed at ART Fertility Clinics, Abu Dhabi between March 2018 and April 2020 and included data of 796 mature oocytes injected from 42 stimulation cycles. Sibling oocytes were randomly split between 2 different incubators: 12 oocytes were assigned to the twelve wells of the EmbryoscopeTM (ES) and the remaining oocytes were cultured in a conventional benchtop incubator, G185 K-System (KS). Participants/materials, setting, methods Embryos from patients with primary or secondary infertility, who underwent ovarian stimulation for ICSI and PGT-A through NGS on trophectoderm biopsies, were eligible. All patients had at least 16 fresh mature oocytes, randomly allocated to two different incubators after ICSI: 503 (63.2%) oocytes were cultured in ES and 293 (36.8%) in KS. The fertilization, cleavage, useable blastocyst and euploid rates, as well as embryo/blastocyst qualities were assessed to evaluate each incubator’s performance. Main results and the role of chance The fertilization and cleavage rates were similar between incubators. Total useable blastocyst rate (64.8% vs 49.6%, p Limitations, reasons for caution The current observational study needs confirmation in a prospective trial and should also include the implantation potential of the euploid blastocysts, which was not followed in the current study. A good prognosis population (≥16 mature oocytes) was studied and may not reflect the outcomes in patients with lower oocyte numbers. Wider implications of the findings: This work builds evidence to the solid introduction of the TLT incubators to the clinical routine, as the reduced exposure of embryos outside the incubator – and hence decreased stress - improves the blastocyst development. Trial registration number NA

Study question Is parental consanguinity associated with reduced ovarian reserve in women from the Arabian Peninsula? Summary answer: Women descending from consanguineous unions have a reduced ovarian reserve compared with daughters of non-consanguine couples. What is known already Consanguineous marriage is defined as marriage between second-degree cousins or closer, with high prevalence in the Arabian Peninsula societies. An increased incidence of autosomal recessive diseases has been described in consanguineous marriages compared with non-consanguineous marriages. Despite the known adverse genetic impact of consanguinity, most available studies focus on the fertility of the consanguine couple. Only few publications, including low number of women, evaluated the impact of consanguinity on the fertility of their offspring, suggesting that daughters of consanguine parents might have reduced fertility associated to reduced ovarian reserve. Study design, size, duration A retrospective large-scale observational study was performed including 2482 women from the Arabian Peninsula who had their serum AMH and AFC measured as part of their fertility assessment at ART Fertility Clinics (UAE and Oman), from May 2015 to November 2019. Participants/materials, setting, methods 2482 women from the Arabian Peninsula, aged 19–50 years, were assessed. Consanguinity was defined as women whose parents were first-degree or second-degree cousins. Ovarian reserve was evaluated by Antral Follicle Count (AFC) with transvaginal ultrasound and serum AMH, measured by Elecsys (Cobas, Roche®) for all participants. Women with adnexal surgery history or/and hormonal treatment within previous three months (n = 284) were excluded. Ethical approval was obtained from the Research Ethics Committee (REFA040). Main results and the role of chance After excluding women with previous adnexal surgeries, 2198 women were included for analysis. A total of 605 participants (27.53%) were descendants from consanguineous unions and 1593 (72.47%) reported non-consanguineous kinship of their parents. AMH and AFC (mean±SD) for the consanguineous group were 2.62±2.88 ng/mL and 12.78±9.73 antral follicles, respectively; and AMH and AFC (mean±SD) for the non-consanguineous group were 2.65±2.91 ng/mL and 13.07±9.39 antral follicles, respectively. Women from the consanguinity group were significantly younger (mean±SD: 33.74±6.64 years old) compared with the non-consanguinity group (mean±SD: 34.78±6.64 years old, p Limitations, reasons for caution Despite the large number of women included, the retrospective study design is a limitation. Results have to be treated with caution before translating into other populations, as these data are obtained from women native to the Arabian Peninsula, with high sociocultural/religious/ethnical similarities, which might differ to other consanguine populations. Wider implications of the findings: Female parental consanguinity is associated with reduced ovarian reserve in the studied population, that might contribute to infertility. Future studies should examine the genetic and epigenetic basis of the current findings. Comprehensive clinical evaluation should include extensive family history and subsequent counselling of the affected couples. Trial registration number Not applicable

Study question Frozen embryo transfer (FET) of euploid blastocysts in hormone replacement therapy (HRT) or natural cycle (NC): are there differences in obstetric, fetal and neonatal outcomes? Summary answer Pregnancy complications, neonatal outcomes and fetal abnormalities are not increased after FET with PGT-A in singleton pregnancies. What is known already Since its introduction, PGT has been widely used in ART centers for preventing chromosomal and monogenic diseases. Despite its increased use, there are scarce and conflicting data about adverse pregnancy, fetal and neonatal outcomes. In one published study, the risk of preeclampsia and placenta previa was increased when PGT pregnancies were compared with non-PGT, while the incidence of gestational diabetes mellitus (GDM), preterm delivery, fetal defects and NICU (Neonatal Intensive Care Unit) admission were similar. According to other data, the rate of caesarean section in PGT pregnancies was high - around 80% in singletons. Study design, size, duration An observational, retrospective study was conducted between March 2015 and November 2019 in patients with singleton pregnancies after ART with PGT-A/FET/HRT and NC. A total number of 353 patients from two fertility centers (ART Fertility Clinics Dubai and Abu Dhabi, UAE), were included. They were divided into two groups according to the endometrial preparation for FET: group A: HRT (n = 225) and group B: NC (n = 128). Participants/materials, setting, methods Patients with primary / secondary infertility and at least one transferable euploid blastocyst after trophectoderm biopsy, achieving an ongoing singleton pregnancy after FET were included. Endometrial preparation for FET was either performed in a NC or an HRT cycle. For this study, the following pregnancy outcomes were recorded: GDM, preeclampsia and hypertension, obstetric cholestasis, placental abnormalities, mode of delivery, preterm delivery, gestational age at delivery, birth weight, fetal abnormalities and admission to NICU. Main results and the role of chance There were no statistically significant differences in maternal and demographic characteristics of the studied groups. The mean maternal age was 34.05(20–45) and 34.26(23–47) years for group A and B respectively. The mean BMI was 28.31kg/m² (17.93–43.76) versus 27.93 (17.32–43.18). The ratio of nulliparous versus multiparous patients was 1:1 for both groups. Majority of the patients in both groups were of Arab ethnicity. The number of patients recorded as smokers was low and comparable in the groups. The mean gestational age at the time of delivery was comparable: 37.64 gestational weeks (24–41) versus 37.76 (26–41). The Caesarean section rate was around 50% for both groups. The rate of preterm delivery was comparable in both groups (16.9% and 18.8% for group A and B respectively). There was no detectable difference in the distribution of the birth weight in both groups with a median weight of 3000 grams of which 13.6% were low birth weight. In the studied groups, 30.5% had pregnancy complications with no observed statistically significant differences when the groups were compared. There was no increased incidence of fetal abnormalities. Admission to NICU was comparable and was related to prematurity. Limitations, reasons for caution The limitations of the study are the retrospective design and the small number of participants. Wider implications of the findings: In patients with FET of an euploid embryo after PGT-A, the type of FET treatment preparation (HRT or NC) has no significant effect on pregnancy complications, birth weight and fetal abnormalities. The findings of the present study could be used to improve prenatal counselling for women undergoing ART with PGT-A. Trial registration number Not applicable

Study question Are the ovarian reserve parameters and the outcome of ovarian stimulation for IVF / ICSI influenced by ethnicity? Summary answer Ethnicity influences ovarian reserve parameters and the outcome of ovarian stimulation for IVF / ICSI What is known already Infertility affects couples worldwide and due to a lack of a standardized reporting system, the real number, especially in developing countries, might be underestimated. The etiology of infertility may differ around the world and is often subjected not only to social, cultural and religious peculiarities, but also to different genetic influences. Published data suggest that ethnicity influences the ovarian reserve as well as the outcome of Assisted-Reproductive-Techniques (ART)-treatments. Key players of a successful ART outcome are the ovarian reserve and consequently the number of oocytes retrieved. Until today, the impact of ethnical differences is not sufficiently addressed in research. Study design, size, duration Prospective observational study, performed in 10 infertility centers worldwide (Europe (4 centers), Middle East North Africa (MENA) region (2 centers), Iran (2 centers), South America (1 center), India (1 center)) between May 2019 and September 2020, evaluating ovarian reserve and outcome parameters of ovarian stimulation treatments for IVF/ICSI. The study was approved by the Ethical Committee of each participating center. Participants/materials, setting, methods Couples with primary / secondary infertility and an indication for an IVF/ICSI treatment were included into this study. Besides anamnestic data regarding the history of the infertility and self-reported ethnicity (Arab, Caucasian, Hispanic, Ohters, Persian and South Asian), data obtained during the basic fertility assessment on the ovarian reserve parameters (Antral follicle count (AFC) and Anti-Muellerian-Hormone (AMH)) as well as stimulation parameters from the ovarian stimulation treatment were collected and analyzed. Main results and the role of chance This study comprised 1032 couples with the following distribution of the ethnicities: Arab 21.5%, Caucasian 15.9%, Hispanic 5%, Others 1.2%, Persian 33.4%, and South Asian 23%. The unadjusted means, SD and 95%CI (Confidence Interval) of AMH (ng/ml) for the groups were 3.33±0.19 [2.95–3.71]; 2.03±0.25 [1.55–2.52]; 2.43±0.74 [0.97–3.88]; 2.76±0.96 [0.88–4.64]; 3.10±0.16 [2.79–3.41]; 3.62±0.19 [3.25–3.98], for AFC 15.52±0.53 [14.49–16.55]; 12.00±0.67 [10.69–13.31]; 12.69±1.08 [10.57–14.81]; 15.11±2.60 [10.01–20.21]; 13.58±0.42 [12.75–14.41]; 13.49±0.51 [12.49–14.48] and for the number of retrieved oocytes (rCOC) 14.08±0.61 [12.88–15.27]; 9.84±0.71 [8.44–11.24]; 7.94±1.26 [5.48–10.41]; 9.92±2.62 [4.78–15.05]; 10.83±0.49 [9.87–11.79]; 17.06±0.59 [15.90–18.21], respectively. Univariate analysis of AMH, AFC and rCOC with the ethnicities revealed highly statistically significant differences for AMH and rCOC (p As age is a major confounder for the ovarian reserve, multivariate analyses were performed. After adjusting for age, AMH was significantly different between Arab-Persian, Arab-South Asian and Arab-Caucasian (p Limitations, reasons for caution Limitations of the study are an unequal number of included patients per ethnicity and that the data for the ovarian reserve parameters and the stimulation outcome were not available for all of the included patients. Wider implications of the findings: Counselling of couples with infertility have to take, besides all other factors, also the ethnicity of the couple into account as ethnicity influences the ovarian reserve parameters as well as the number of retrieved oocytes in ovarian stimulation cycles for IVF/ICSI. Trial registration number ClinicalTrials.gov Identifier: NCT03927417

Study question Does the ratio of serum progesterone (P4) to the number of follicles (P4/Follicle) on the day of final oocyte maturation affect the ploidy status of the embryos? Summary answer A high P4/Follicle ratio negatively affects the euploid rate of the embryos. What is known already During ovarian stimulation, exogenous gonadotropins are administered to achieve multifollicular growth. Intense gonadotropin stimulation towards the end of the follicular phase seems to cause a premature progesterone rise in stimulated IVF cycles. The impact of serum progesterone elevation during the follicular phase has been studied intensively. Though most studies have focused on the effect of progesterone elevation on the endometrial receptivity, little is known about its possible impact on embryo development and ploidy status. The only study that investigated the effect of progesterone on the embryo ploidy status, was unable to show any significant impact. Study design, size, duration This retrospective study was performed at ART Fertility Clinics Abu Dhabi, UAE and Muscat, Oman. All stimulation cycles (n = 975) were performed between January 2015 to December 2019 with patients aged between 18–45, Body mass index (BMI) of 18–35, stimulated either with rFSH or hMG. All embryos underwent ICSI and Preimplantation Genetic Testing for Aneuploidies (PGT-A),Patients with surgical sperm extraction, warmed oocytes or natural cycle IVF were excluded. Participants/materials, setting, methods Serum P4 was measured on the last ultrasound prior triggering for final oocyte maturation. The P4/Follicle ratio was calculated as the ratio of P4 on trigger day to the number of follicles > 10 mm on the last ultrasound. Serum P4 and P4/Follicle ratio were then analyzed using linear and univariate regression model to find potential correlation with the number of oocytes retrieved, number of mature oocytes, embryo quality (day 3 and 5), and euploid rate. Main results and the role of chance A total of 975 cycles were analyzed, with a mean age of 33.88±0.05 years, a mean BMI of 26.7±0.035 kg/m2. The mean number of oocytes collected was 12.53±0.058. Mean serum P4 on trigger day was 0.83±0.005 ng/ml and higher serum P4 values were observed as the number of oocytes retrieved and the number of mature oocytes increased (β = 0.026, p While day 3 embryos were not affected by serum P4 or P4/Follicle ratio, the blastocyst quality was negatively affected by both increasing serum P4 levels and the P4/Follicle ratio (β=–0.012 p Euploid rates were positively correlated in cycles with increased serum P4 β = 0.18, p After adjusting for potential confounders, only P4/Follicle remained as a significant negative factor for euploid rate (β=–0.004, p Limitations, reasons for caution This is an observational study based on retrospective data; an improved extrapolation of the results might be obtained by performing a prospective study. Wider implications of the findings: The findings of this study should encourage clinicians to optimize the ovarian stimulation protocols not only based on serum P4, but also considering the P4/Follicle ratio. Trial registration number Not applicable

Study question Do delayed mature oocytes result in similar euploid blastocyst rates as their immediate mature sibling oocytes? Summary answer Once a blastocyst is obtained, delayed mature oocytes have similar euploid rates compared to immediate mature oocytes. What is known already Intracytoplasmic sperm injection (ICSI) of metaphase II oocytes few hours post oocyte retrieval is standard practice in IVF laboratories. Immature metaphase I (MI) and prophase I (GV) oocytes are usually discarded. Immature oocytes may mature overnight, after which ICSI can be performed. Studies demonstrated lower fertilization and blastulation rates for these delayed mature oocytes. However, live births have been reported from blastocysts transferred. The evidence available is not compelling, since most of the studies had either low sample size, no preimplantation genetic testing for aneuploidies (PGT-A), or the outcome was not compared to sibling MII oocytes at time of denudation. Study design, size, duration A single-center retrospective sibling oocyte study was performed between January 2019 and December 2020 at ART Fertility clinics Abu Dhabi, UAE. A total of 345 PGT-A cycles, with at least one delayed mature oocyte inseminated by ICSI, were included: 2506 immediate mature oocytes and 669 delayed mature oocytes. Participants/materials, setting, methods Following controlled ovarian stimulation, MII oocytes at the time of denudation were inseminated by ICSI/IVF (immediate mature). Immature oocytes (MI/GV) were cultured for 16–24 hours in fertilization medium and injected the next day if matured (delayed mature). Trophectoderm biopsy was performed on day 5/6/7 and samples were subjected to Next Generation Sequencing to screen the ploidy state of the blastocyst. Main results and the role of chance The 345 controlled ovarian stimulation cycles resulted in the insemination of 2506 MII oocytes on the day of oocyte retrieval (Day0) and 669 delayed mature oocytes on day 1. Normal fertilization rate was significantly higher in the immediate mature oocytes compared to delayed mature oocytes (68% vs 56%, p Fisher’s Exact Test was performed to compare the euploid rate of blastocysts biopsied on day 5/6/7 originating from immediate mature oocytes or sibling delayed mature oocytes. The euploid potential of blastocyst biopsied showed no significant difference between the two groups (p = 0.388). Limitations, reasons for caution The timing of MI/GV oocytes transition to MII stage was not recorded since the incubation was done in a benchtop incubator. Furthermore, the same sperm sample was used to inseminate immediate and delayed mature oocytes, which might contribute to the compromised embryo development due to increased sperm DNA fragmentation. Wider implications of the findings: Insemination of delayed mature oocytes by ICSI, should be considered as a tool to increase patients’ chances of obtaining a euploid embryo. Especially in cases where low yield of euploid embryos is expected. Trial registration number Not applicable

Study question Is the live birth rate (LBR) in euploid frozen embryo transfer (FET) cycles affected by the endometrial thickness (EMT)? Summary answer A significantly higher LBR was observed in patients with an endometrial thickness of at least 7.5mm (46.24% vs. 54.63%) What is known already Parameters assessing the endometrium prior planning a FET include endometrial thickness, pattern and blood flow. The impact of the endometrial thickness on ART outcomes is controversial, with conflicting results published. A recent meta-analysis evaluated whether EMT could predict pregnancy outcomes and suggested that lower EMT was associated with lower incidence of clinical pregnancy rate (CPR), implantation rate (IR) and LBR. Due to heterogeneity of parameters evaluated between different publications, where embryos with unknown ploidy status were transferred, in conjunction with variability of stimulation protocols and the number of embryos transferred, the real effect of the EMT was difficult to infer. Study design, size, duration This was a two-center retrospective observational study including a total of 1522 euploid FET cycles between March 2017 and March 2020 at ART Fertility Clinics Muscat, Oman and Abu Dhabi, UAE. Participants/materials, setting, methods Trophectoderm biopsies were analyzed with Next Generation Sequencing (NGS). Vitrification/warming of blastocysts was performed using Cryotop method (Kitazato). EMT was measured by vaginal ultrasound prior initiating the progesterone administration (± 1 day) and LBR was recorded. Multivariate analysis was performed between LB outcomes and median EMT while controlling for confounding factors. Main results and the role of chance A total of 1522 FET cycles were analyzed: 975 single embryo transfer (SET) and 547 double embryo transfer (DET). The mean age of the patients was 33.38 years with a mean BMI of 27.1 kg/m2. FET were performed in EMT ranging from 3 to 15 mm and 50.52% resulted in a live birth. Though potentially all ranges of EMT were associated with LB, the median EMT in patients with LB was significantly higher than the median EMT of patients without LB (7.6mm vs. 7.4mm; p The dataset was stratified into two groups based on the median EMT (7.5mm): < 7.5mm (n = 744 cycles) and ≥ 7.5mm (n = 778 cycles). A significantly higher live birth rate was observed in ≥ 7.5mm group (46.24% vs. 54.63%. p = 0.0012). In multivariate analysis, EMT, FET endometrial preparation protocol, and number of embryos transferred were the main parameters influencing the chance to achieve LB: OR 1.10 [1.01–1.19], p Limitations, reasons for caution Besides the retrospective nature of the study, the inter-observer variability in EMT assessment between different physicians is a limitation. The physician and embryologist performing the embryo transfer could not been standardized due to the multicenter design of the study. Wider implications of the findings: The EMT in FET may influence the LBR and should be considered as an important factor for the success of embryo transfer cycles. Whether these results can be extrapolated to fresh embryo transfer and to blastocysts with unknown ploidy status, needs further investigation. Trial registration number Not applicable