Lucovnik M, et al. - The effect of pre-gravid body mass index (BMI) on perinatal outcomes was examined in in vitro fertilization (IVF) singleton pregnancies. In this retrospective population-based cohort study including all singleton pregnancies delivered at ≥ 22 weeks’ in Slovenia between 2002 and 2015, pre-gravid overweight and obesity were noted to be associated with higher rates of hypertensive disorders, gestational diabetes, and cesarean deliveries in both IVF and non-IVF pregnancies. Observations also suggested an association of pre-gravid underweight with small for gestational age neonates in IVF and non-IVF pregnancies. Findings thereby signify an important effect of pre-gravid BMI on perinatal outcomes in pregnancies following IVF.