VP34.02: The effect of maternal BMI, across the BMI spectrum, on fetal growth and adiposity

Maternal overweight and obesity, defined as BMI ≥25 kg/m2 and BMI ≥30.0 kg/m2 respectively, represent a significant public health burden globally, and rates are rapidly increasing across developed nations. Very little is known about fetal growth and fetal growth trajectories in this high risk population. We aimed to examine the effect of increasing maternal BMI, across the BMI spectrum, on fetal growth and adiposity measures and their trajectories, among a prospectively recruited, contemporary cohort of Australian women. We also aimed to characterise the nature of the relationship between maternal BMI and fetal growth and adiposity measures. This was a secondary analysis of results from two contemporary randomised controlled trials, the LIMIT and Optimise randomised trials. Participants were pregnant women with a BMI of >/= 18.5kg/m2, and a singleton gestation between 10+0 and 20+0 weeks. Data were obtained from research ultrasounds, performed at 28 and 36 weeks of gestation, of participants randomised to the Standard Care groups of these trials. The total sample size consisted of 1,377 women who underwent one or more fetal ultrasounds over the course of their pregnancy. Maternal BMI ranged from 18.5-24.9 kg/m2 (n = 317 women; 23/02%) up to >/= 40 kg/m2 (n = 122 women; 8.86%). Assessment of the relationship between maternal BMI and fetal growth measures did not provide any evidence of nonlinear relationships, and indicated that linear regression models were optimal. For all fetal biometry measures except for fetal femur length, we found statistically significant positive associations with increasing maternal BMI at each timepoint. At 36 weeks of gestation, we found a statistically significant association with increasing maternal BMI and increasing fetal adiposity measures of mid-thigh fat mass, abdominal fat mass, abdominal area, and subscapular fat mass. We show a positive linear relationship between maternal BMI, across the BMI spectrum, and fetal growth and adiposity.