Maternal pre-pregnancy body mass index (BMI) and gestational weight gain are factors influencing neonatal birth weight. Underweight women have a higher risk of spontaneous preterm birth and small for gestational age infants. Whether underweight women at the time of delivery have the same risks, regardless of pre-pregnancy weight and weight gain during pregnancy, has not been reported for our region.
Ideal weight was defined as a BMI greater than 18.4 and less than 25. Underweight was defined as a BMI less than 18.5. The pre-pregnancy weight and weight gain were not included. This was a retrospective study of all deliveries at our hospital from 12/14/2009 to 10/1/2013 greater than 23 weeks. There was a total of 45,961 singleton deliveries. Thirty-six women were underweight versus 5,343 women considered ideal weight at the time of delivery.
Major demographic variables were similar between the groups. Rates of preterm birth were higher in the underweight group (P < .05). Rates of induction of labor were higher in the ideal weight group (P < .05). There was no difference in cesarean section rates, Apgar’s, or cord pH. The neonatal birth weight was significantly smaller for the underweight patients (P < .05). However, the rate of NICU admissions was significantly higher in the underweight group vs the ideal weight (P < .05).
Maternal weight at birth has the same implication on prematurity and low birth weight as maternal pre-pregnancy weight when underweight women are compared to ideal weight women.