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STUDY QUESTION What were the risks with regard to the pregnancy outcomes of patients who conceived by frozen-thawed embryo transfer (FET) during a hormone replacement cycle (HRC-FET)? SUMMARY ANSWER The patients who conceived by HRC-FET had increased risks of hypertensive disorders of pregnancy (HDP) and placenta accreta and a reduced risk of gestational diabetes mellitus (GDM) in comparison to those who conceived by FET during a natural ovulatory cycle (NC-FET). WHAT IS KNOWN ALREADY Previous studies have shown that pregnancy and live-birth rates after HRC-FET and NC-FET are comparable. Little has been clarified regarding the association between endometrium preparation and other pregnancy outcomes. STUDY DESIGN, SIZE, DURATION A retrospective cohort study of patients who conceived after HRC-FET and those who conceived after NC-FET was performed based on the Japanese assisted reproductive technology registry in 2014. PARTICIPANTS/MATERIALS, SETTING, METHODS The pregnancy outcomes were compared between NC-FET (n = 29 760) and HRC-FET (n = 75 474) cycles. Multiple logistic regression analyses were performed to investigate the potential confounding factors. MAIN RESULTS AND THE ROLE OF CHANCE The pregnancy rate (32.1% vs 36.1%) and the live birth rate among pregnancies (67.1% vs 71.9%) in HRC-FET cycles were significantly lower than those in NC-FET cycles. A multiple logistic regression analysis showed that pregnancies after HRC-FET had increased odds of HDPs [adjusted odds ratio, 1.43; 95% confidence interval (CI), 1.14–1.80] and placenta accreta (adjusted odds ratio, 6.91; 95% CI, 2.87–16.66) and decreased odds for GDM (adjusted odds ratio, 0.52; 95% CI, 0.40–0.68) in comparison to pregnancies after NC-FET. LIMITATIONS, REASONS FOR CAUTION Our study was retrospective in nature, and some cases were excluded due to missing data. The implication of bias and residual confounding factors such as body mass index, alcohol consumption, and smoking habits should be considered in other observational studies. WIDER IMPLICATIONS OF THE FINDINGS Pregnancies following HRC-FET are associated with higher risks of HDPs and placenta accreta and a lower risk of GDM. The association between the endometrium preparation method and obstetrical complication merits further attention. STUDY FUNDING/COMPETING INTEREST(S) No funding was obtained for this work. The authors declare no conflicts of interest in association with the present study. TRIAL REGISTRATION NUMBER Not applicable.

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Recent studies have suggested that intrauterine undernutrition is closely associated with the pathogenesis of diseases after birth. Perinatal undernutrition is known to disturb the development of reproductive function and delay the onset of puberty in some species. Using a rat model, we determined the effects of prenatal undernutrition on the development of the hypothalamic kisspeptin system and evaluated whether the alteration of the kisspeptin system contributes to the delayed onset of puberty induced by prenatal undernutrition. We also evaluated the effects of prenatal undernutrition on the developmental changes in serum leptin levels because leptin was a putative positive regulator of the hypothalamic kisspeptin system. We compared the timing of vaginal opening (VO) and the developmental changes in body weight, hypothalamic Kiss1 mRNA levels, and serum leptin concentrations between offspring with prenatal undernutrition (UN offspring) and normal nutrition (NN offspring). After birth, the UN offspring showed rapid growth and had caught up to body weight of the NN offspring by postnatal day 12. After postnatal day 16, the UN offspring showed significantly lower Kiss1 mRNA levels than the NN offspring, despite their significantly higher serum leptin levels (at days 20 and 28). The timing of VO in the UN offspring was delayed compared with that in the NN offspring, and chronic central injection of kisspeptin normalized the timing of VO in the UN offspring. These results suggest that decreased hypothalamic kisspeptin action contributes to the delayed onset of puberty in prenatally undernourished female rats. Increased leptin resistance in the kisspeptin system might be involved in these alterations.