STUDY QUESTION Can the endometrial thickness (EMT) on the day of the LH surge predict pregnancy outcomes after single vitrified-warmed blastocyst transfers (SVBTs) in modified natural cycles? SUMMARY ANSWER Decreased EMT on the day of the LH surge is associated with older female age and a shortened proliferation phase and may be associated with low live birth and high chemical pregnancy rates. WHAT IS KNOWN ALREADY The relation between EMT on the day of embryo transfer (ET) and pregnancy outcomes remains controversial; although numerous studies reported an association between decreased EMT on the day of ET and a reduced likelihood of pregnancy, recent studies demonstrated that the EMT on the day of ET had limited independent prognostic value for pregnancy outcomes after IVF. The relation between EMT on the day of the LH surge and pregnancy outcomes after SVBT in modified natural cycles is currently unknown. STUDY DESIGN, SIZE, DURATION In total, 808 SVBTs in modified natural cycles, performed from November 2018 to October 2019, were analysed in this retrospective cohort study. Associations of EMT on the days of the LH surge with SVBT and clinical and ongoing pregnancy rates were statistically evaluated. Clinical and ongoing pregnancy rates were defined as the ultrasonographic observation of a gestational sac 3 weeks after SVBTs and the observation of a foetal heartbeat 5 weeks after SVBTs, respectively. Similarly, factors potentially associated with the EMT on day of the LH surge, such as patient and cycle characteristics, were investigated. PARTICIPANTS/MATERIALS, SETTING, METHODS The study includes IVF/ICSI patients aged 24–47 years, who underwent their first SVBT in the study period. After monitoring follicular development and serum hormone levels, ovulation was triggered via a nasal spray containing a GnRH agonist. After ovulation was confirmed, SVBTs were performed on Day 5. The EMT was evaluated by transvaginal ultrasonography on the day of the LH surge and immediately before the SVBT procedure. MAIN RESULTS AND THE ROLE OF CHANCE Of the original 901 patients, 93 who were outliers for FSH or proliferative phase duration data were excluded from the analysis. Patients were classified according to quartiles of EMT on day of the LH surge, as follows: EMT < 8.1 mm, 8.1 mm ≤ EMT < 9.1 mm, 9.1 mm ≤ EMT < 10.6 mm and EMT ≥ 10.6 mm. Decreased EMT on day of the LH surge was associated with lower live birth ( P = 0.0016) and higher chemical pregnancy ( P = 0.0011) rates. Similarly, patients were classified according to quartiles of EMT on day of the SVBT, as follows: EMT < 9.1 mm, 9.1 mm ≤ EMT < 10.1 mm, 10.1 mm ≤ EMT < 12.1 mm and EMT ≥ 12.1 mm. A decreased EMT on the day of SVBT was associated with a lower live birth rate ( P = 0.0095) but not chemical pregna...

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STUDY QUESTION Is the embryo transfer method associated with maternal and perinatal outcomes after minimal stimulation IVF using clomiphene citrate (CC)? SUMMARY ANSWER The incidence of pregnancy complications and adverse perinatal outcomes was influenced by the developmental stage (cleavage versus blastocyst stages) and cryopreservation (fresh versus vitrified) of the transferred embryos. WHAT IS KNOWN ALREADY Pregnancies resulting from IVF are associated with higher risks of adverse perinatal outcomes compared to natural conceptions; therefore, the next focus in reproductive medicine should be to assess whether these increased risks are attributable to IVF. Pregnancy complications and perinatal outcomes should be considered in addition to pregnancy outcomes when selecting the embryo transfer method, however studies that describe the influence of transfer methods on perinatal and maternal outcomes are limited. STUDY DESIGN, SIZE, DURATION This study retrospectively analysed a large single-centre cohort. The clinical records of 36,827 women who underwent oocyte retrieval (during a CC-based minimal stimulation cycle) followed by their first embryo transfer at the fertility treatment centre between January 2008 and December 2017 were retrospectively analysed. The patients underwent a single fresh cleavage-stage embryo transfer (SFCT), single vitrified-warmed cleavage-stage embryo transfer (SVCT), or single vitrified-warmed blastocyst transfer (SVBT). This study only included one cycle per patients. PARTICIPANTS/MATERIALS, SETTING, METHODS Oocyte retrieval was performed following CC-based minimal ovarian stimulation. The embryos were transferred 2–3 days after retrieval or vitrified at the cleavage or blastocyst stage. The vitrified embryos were then warmed and transferred within the natural cycles. Pregnancy complications and perinatal outcomes were stratified according to the transfer methods used. Multivariate logistic regression analysis was performed to evaluate the effect of embryo transfer methods on the prevalence of pregnancy complications and congenital anomalies. MAIN RESULTS AND THE ROLE OF CHANCE The rates of clinical pregnancy and delivery were significantly different among the groups. We analysed pregnancy complications in 7,502 singleton births (SFCT, 3,395 cycles; SVCT, 586 cycles; and SVBT, 3,521 cycles). Multivariate logistic regression analysis revealed that the adjusted odds ratio (AOR) for hypertensive disorders in pregnancy was significantly lower in the SVBT group than in the SFCT group [AOR, 0.72; 95% CI, 0.56–0.92]. The AOR for low-lying placenta was lower in the SVBT group than in the SFCT group (AOR, 0.34; 95% CI, 0.19–0.60). The AOR for placenta previa was lower in the SVCT and SVBT groups than in the SFCT group (AOR, 0.21; 95% CI, 0.07–0.58 versus AOR, 0.53; 95% CI, 0.38–0.75, respectively). A total of 7,460 follow-up data on neonatal outcomes was analysed. The AOR for preterm delivery was lower in the SVBT group than in the SFCT group (AOR, 0.78; 95% CI, 0.64–0.94). The AOR for low birthweight was significantly lower after SVCT and SVBT than after SFCT (AOR, 0.68; 95% CI, 0.46–0.98 versus AOR, 0.57; 95% CI, 0.48–0.66, respectively). The AOR for SGA was lower in the SVCT and SVBT groups than in the SFCT group (AOR, 0.68; 95% CI, 0.46–0.98 versus AOR, 0.44; 95% CI, 0.36–0.55, respectively). The AOR for LGA babies was higher in the SVBT group than in the SFCT group (AOR, 1.88; 95% CI, 1.62–2.18). The incidence of each congenital anomaly was similar among the groups. LIMITATIONS, REASONS FOR CAUTION The study data were collected through self-reported parental questionnaires on maternal and neonatal outcomes. Our findings were not compared with the incidence of pregnancy complications and congenital anomalies in natural pregnancies. Furthermore, this study was retrospective in nature; therefore, further studies are required to ascertain the generalisability of these findings to other clinics with different protocols and/or different patient demographics. WIDER IMPLICATIONS OF THE FINDINGS This study demonstrated reassuring outcomes for SVBT (in terms of a lower incidence of pregnancy complications) compared to SFCT. Our findings provide valuable knowledge that will help improve perinatal and maternal outcomes in CC-based stimulation and inform couples of the possible benefits and risks of each type of embryo transfer method. STUDY FUNDING/COMPETING INTEREST(S) This research did not receive any specific grants from funding agencies in the public, commercial, or not-for-profit sectors. The authors have no conflicts of interest to declare. TRIAL REGISTRATION NUMBER N/A.

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Aim To investigate the clinical factors and factors that affect the decisions regarding storage of cryopreserved embryos obtained using assisted reproductive technology. Methods Clinical characteristics affecting the decisions regarding cryopreserved embryos were analyzed in 5724 Japanese couples who underwent in vitro fertilization (IVF) or intra‐cytoplasmic sperm insemination (ICSI) and embryo transfer over 4 years since April 2015 at our clinic. Statistical analysis was carried out using JMP software. Results The number of oocytes retrievals and embryos stored, outcomes and number of children, and age of the female patients and male partners were related to the decision‐making regarding cryopreserved embryos. Childbearing and no wish for another child were the major reasons for discontinuing embryo storage. The number of oocytes retrievals and embryos in storage, age of the female patients, and sex of the child were independently associated with this decision‐making in 2682 patients with a single child. Women with male children were more likely to choose discontinuation of embryo storage than those with female children. Conclusion Already having a child and not wishing for further treatment due to age along with the presence of a male child affect the decision to continue or discontinue embryo storage in Japanese patients with infertility.