Presentation (CTI)

OBJECTIVES: This study assessed maternal weight trajectories across pregnancy to delivery and examined the association between gestational weight change (GWC) and newborn birthweight.
METHODS: Using a subset of electronic health records from Truveta Data, mothers aged 18-50 who gave birth to a term, singleton infant from 2019-2025 were followed over their first recorded pregnancy to evaluate weight change. Mothers were required to have weight records at baseline, first trimester, and two weeks before delivery. Baseline weight and BMI were defined as measurements closest to 40 and no more than 37 weeks before delivery. Infant weights were required within one day of birth. Extreme values (<3lb 5oz or >13lb 4oz) were excluded. GWC and infant birthweight were summarized overall and by maternal baseline BMI.
RESULTS: We included 117,752 pregnant mothers and their linked infants. Mothers had an average of 12 weight measurements during pregnancy, with a median weight gain of 30 pounds. Among those who lost weight at some point during pregnancy, the median weight loss was 4.9 pounds. The median newborn birthweight was 7.2 pounds. Forty-five percent of mothers had evidence of weight loss, primarily in the first trimester. Weight gain decreased with increased baseline BMI; mothers with underweight or normal BMI gained a median 34.0 pounds, and women with overweight and obese BMI gained 31.0 and 23.5 pounds, respectively. Median infant weight was 7.0 pounds for mothers who gained 0-15 pounds, 7.4 pounds for mothers who gained 35-45 pounds, and 7.8 pounds for mothers who gained 80-100 pounds. Among mothers without obesity, those gaining 0-15 pounds had the highest low-birth-rate (LBW, <2,500 g) rate (12.6%).
CONCLUSIONS: Greater GWC during pregnancy was associated with higher birthweight, while maternal weight loss was associated with lower birthweight. Mothers who gained <15 pounds had increased probability of delivering a LBW infant.