Obesity During Pregnancy Increases Risk of Macrosomia

Cuilin Zhang MD

Cuilin Zhang MD, MPH

Independent of conditions like hypertension and diabetes, obesity during pregnancy places women at a higher risk of having an infant with macrosomia, a condition characterized by atypically large body size at birth, according to a new study published in JAMA Pediatrics.

In cohorts of 443 obese women and 2320 non-obese women, study authors found that both fetal femur length and humerus length were significantly longer for fetuses of obese women than those in non-obese women, and that these differences persisted from 21 weeks’ through 38 weeks’ gestation (median femur length, 71.0 vs 70.2mm, p=0.01; median humerus length 62.2 vs 61.6mm, p=0.03).

When averaged across gestation, head circumference was significantly larger in fetuses of obese women than those in non-obese women (p=0.02), however, fetal abdominal circumference was not greater in the obese cohort than in the non-obese cohort, but was significantly larger than in fetuses of normal-weight women with body mass indexes (BMI) between 19.0-24.9.

Moreover, starting from 30 weeks’ gestation, estimated fetal weight was significantly larger for the fetuses of obese women (median 1512 g [95% CI, 1494-1530 g] versus 1492 g [95% CI, 1484-1499 g]), with the difference growing as gestational age increased.

“Other studies have shown that babies born to obese women are likely to develop childhood obesity. Our results suggest that obese women — even those without chronic diseases such as hypertension, diabetes and cardiovascular diseases – should strive for a healthy weight before becoming pregnant. During pregnancy, they should carefully monitor their weight and try not to gain too much weight,” said Ciulin Zhang, MD, MPH, of the Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health (NIH).

For the study, Zhang and colleagues recruited 468 obese women (prepregnancy BMI > 30) and 2334 non-obese women (prepregnancy BMI 19-29.9) without major chronic diseases between 8 weeks’ and 13 weeks’ gestation. After prior exclusion criteria, 443 obese and 2320 non-obese women composed the final cohort.

A mixed longitudinal randomization scheme randomized participants into 1 of 4 schedules for 2-dimensional and 3-dimensional ultrasonograms to capture weekly fetal growth data throughout the remainder of their pregnancies.

The study did not determine why the fetuses of obese women were larger and heavier than fetuses in the non-obese group, however, according to an NIH statement, researchers theorize that because women are more likely to have insulin resistance, higher blood sugar levels could have promoted overgrowth in their fetuses.

The authors called for additional studies to follow children born to obese women to determine what health issues they may face, because mechanisms and long term health implications are not yet established.

The study, Associations of Maternal Obesity With Longitudinal Ultrasonographic Measures of Fetal Growth: Findings from the NICHD Fetal Growth Studies-Singletons was published in JAMA Pediatrics on November 13, 2017.

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