The pre-pregnancy BMI and the gestational weight gain are two important determinants of pregnancy outcomes. The aim of this study was to determine obstetric outcomes associated with insufficient gestational weight gain in women with a pre-pregnancy BMI < 18.5 kg/m2. This study was based on observational routinely collected data from University Hospital Maternity. The participants were allocated to the group sufficient or insufficient gestational weight gain: ≥12.5 kg and <12.5 kg respectively. Primary outcomes were the adjusted birth weight in percentiles (%) and the proportion of SGA newborns. Secondary outcomes were obstetric and perinatal outcomes. A total of 132 participants with a median age of 28 ± 8 years were included. The adjusted birth weight in percentiles was significantly lower in the insufficient gestational weight gain group (27.3 ± 45.0 vs. 46.3 ± 46.2%; p < 0.001). Moreover, the insufficient gestational weight gain is associated with a higher risk of SGA (27.0% vs. 11.6%; p = 0.03). Our study also showed increased risks of premature rupture of membranes, anaemia, and intrauterine growth restriction in women with an insufficient weight gain. Future studies should explore the risk factors associated with insufficient weight gain, in order to develop specific care for underweight pregnant women.
Keywords: birth weight; foetal growth restriction; newborn; obstetric outcome; pregnancy; thinness.