Introduction Reproductive scientists have postulated various risk factors for lower birthweight following conventional gonadotropin‐stimulated in vitro fertilization compared with spontaneously conceived children: parental factors (age, health, duration of subfertility and smoking habits); ovarian stimulation; laboratory procedures; the number of oocytes retrieved and the number of embryos transferred. Our aim was to investigate the impact of gonadotropin stimulation and serum estradiol level on the risk of a newborn being small‐for‐gestational‐age. Material and methods We conducted a cohort study (2010‐2016) of singletons (n = 155) born either after conventional gonadotropin‐stimulated in vitro fertilization (using ≥150 IU/d human gonadotropin for stimulation) or after natural cycle in vitro fertilization without any stimulation. We analyzed perinatal outcomes using birthweight percentiles, adjusted for gestational age and sex. Results The proportion of small‐for‐gestational‐age was 11.8% following conventional gonadotropin‐stimulated in vitro fertilization and 2.9% after natural cycle in vitro fertilization (P = 0.058). The odds of small‐for‐gestational‐age were significantly higher with supraphysiological estradiol levels in maternal serum on ovulation trigger day (unadjusted odds ratio 4.58; 95% confidence interval 1.35‐15.55; P = 0.015). It remained significant after adjusting for maternal height, age and body mass index (adjusted odds ratio 3.83; 95% confidence interval 1.06‐13.82; P = 0.041). Conclusions We found an associated risk of children being born small‐for‐gestational‐age after conventional gonadotropin‐stimulated in vitro fertilization compared with natural cycle in vitro fertilization. This higher risk is significantly associated with supraphysiological estradiol levels. We propose a reduction in the dosage of gonadotropin to minimize the risk of small‐for‐gestational‐age and future health consequences.

Aim Breastfeeding has numerous advantages. Our aim was to investigate whether breastfeeding initiation and duration in women with pregnancies conceived through in vitro fertilisation differ from spontaneously conceived pregnancies. Methods This is a comparative cross‐sectional study about breastfeeding behaviour performed at the Bern University Hospital including mothers of singletons conceived by in vitro fertilisation (n = 198) with or without gonadotropin stimulation between 2010 and 2016 (in vitro fertilisation group). They were compared to a population‐based control group (n = 1421) of a randomly selected sample of mothers in Switzerland who delivered in 2014. Results A total of 1619 women were included in this analysis. Breastfeeding initiation rates were high, similar between the in vitro fertilisation group (93.4%) and the control group (94.8%). No increased risk of stopping breastfeeding earlier after in vitro fertilisation treatment compared to the control group could be found over the observational period of 12 months (HR = 1.00, 95% CI 0.83‐1.20, P = .984). There was no difference in breastfeeding initiation or duration after gonadotropin‐stimulated vs unstimulated in vitro fertilisation. Conclusion In Switzerland, in vitro fertilisation treatments were not associated with earlier breastfeeding cessation. This result is reassuring for mothers undergoing in vitro fertilisation.

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