RESUMO
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.