PSUN175 Impact of Maternal Low Weight on Pregnancy and Neonatal Outcomes

Underweight body mass index (BMI) is defined as a BMI <18.5 kg/m(2) and a subset of low-weight women also meet DSM-5 criteria for a diagnosis of anorexia nervosa. Although anorexia nervosa is often associated with functional hypothalamic amenorrhea and resultant infertility, when women with anorexia nervosa do conceive, there is an increased risk of obstetrical and delivery complications, and poor neonatal outcomes, such as preterm birth, low birth weight, and smaller size for gestational age (SGA). Few studies have investigated such outcomes in women who are low weight, with or without a diagnosis of anorexia nervosa. The aim of the study was toexamine associations between underweight maternal BMI and pregnancy complications and neonatal outcomes in mothers and infants at a large academic medical center. There was a total of 16,780 mothers who delivered a singleton between 2015-2021 with either a BMI <18.5 kg/m(2) (n=732) or who were normal-weight (18.5 kg/m2 < BMI <25 kg/m(2), n=16,048) at their initial prenatal visit or within six months of that visit. We compared neonatal outcomes and pregnancy/delivery complications in the low-weight versus normal-weight mother-infant pairs. Neonatal outcomes included birthweight, gestational age, NICU stay, preterm birth, and fetal death; pregnancy and delivery complications included pre-eclampsia/eclampsia, premature rupture of membranes (PROM), and post-partum hemorrhage. Median BMI in underweight women was 17.8 [interquartile range: 17.2, 18.1] kg/m2 compared with 22.2 [20.7, 23.6] kg/m2 in normal-weight women. Underweight women were younger (27 [22, 31] years) and less likely to be married or have private insurance (p-value <0.0001 for all). Approximately 22% of the low-weight mothers were African American compared with 13.4% of normal-weight mothers (overall p-value for race/ethnicity <0.0001). Additionally, approximately 22% of infants born to low-weight mothers were SGA and 15% with low birthweight compared with 13.6% and 9% of infants born to normal-weight mothers, respectively (p-value <0.0001 for both SGA and low birthweight). These differences remained significant after adjusting for maternal age, race/ethnicity, marital and insurance status, and maternal depression; after adjusting for these potential confounders, infants born to low-weight mothers had increased risk for SGA (OR=1.23, 95% CI: 1.11-1.36) and low birthweight (OR=1.18, 95% CI: 1.04-1.33) compared with their normal-weight counterparts. In adjusted models, underweight women had decreased risk of PROM (OR=0.85, 95% CI: 0.74-0.98) and post-partum hemorrhage (OR=0.72, 95% CI: 0.54-0.96) compared to normal-weight women. No differences were noted for pre-eclampsia/eclampsia, NICU stay, preterm birth, and fetal death. In summary, underweight BMI during pregnancy is associated with an increased risk of infants who are SGA and low birthweight and a decreased risk for delivery complications including PROM and post-partum hemorrhage. These differences suggest underweight BMI during pregnancy increases the risk for adverse neonatal outcomes, while maternal-related pregnancy outcomes are less affected. Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.