Results of a study of fetal ultrasounds show that maternal obesity has an impact on fetal growth as early as 32 weeks’ gestation. However, the mechanisms behind the association and the implications of the findings, published in JAMA Pediatrics, remain to be determined.
For the longitudinal study, researchers looked at cohort of 443 obese (prepregnancy body mass index [BMI] >30) and 2,320 nonobese pregnant women (prepregnancy BMI 19 to 29.9) at 12 US health care institutions. None of the women had major chronic diseases and their pregnancies all were from 8 weeks, 0 days’ to 13 weeks, 6 days’ gestation. The participants were randomized to 1 of 4 schedules of 2- and 3-dimensional ultrasonograms to capture weekly fetal growth for the remainder of their pregnancies.
The authors measured fetal humerus length, femur length, biparietal diameter, head circumference, and abdominal circumference on each ultrasonogram and estimated fetal growth curves using linea mixed models with cubic splines. Likelihood ratios and Wald tests after adjustment for maternal characteristics were used to look at median differences in fetal measures at each gestational week in obese versus nonobese women.
Fetuses of obese women had significantly longer femurs and humeruses than those of nonobese women, beginning at 21 weeks’ gestation. The differences persisted through 38 weeks’ gestation (median femur length 71.0 vs 70.2 mm; P = .01; median humerus length 62.2 vs 61.6 mm; P = .03). Averaged across gestation, head circumference was significantly larger in fetuses of the obese women versus those in nonobese women (P = .02) Fetuses of the obese women were significantly larger than those of women of normal weight beginning at 32 weeks (median 282.1 vs 280.2 mm; P = .04) Estimated fetal weight was also significantly higher in fetuses of obese women, starting at 30 weeks’ gestation (median 1512 g [95% CI, 1494-1530 g] vs 1492 g [95% CI, 1484-1499g] and it increased with gestational age. In neonates born to obese women, birth weight was higher by almost 100 g than in neonates born to the nonobese women (mean 3373.2 vs 3279.5 g).