BMI, Gestational Weight Gain Most Predictive of Macrosomia


SAN FRANCISCO— Prepregnancy body mass index and gestational weight gain are more predictive of fetal macrosomia than homeostasis model assessment and glucose load, a study has shown.

Because both of these are modifiable risk factors, “they should be emphasized in order to minimize the risk of macrosomia and associated adverse outcomes,” reported Dr. Chloe A. Zera in a poster presentation at the annual meeting of the Society for Maternal-Fetal Medicine.

In a prospective study designed to investigate whether either early or late gestational insulin resistance predicts infant birth weight and risk of macrosomia-related cesarean delivery, Dr. Zera of Boston's Brigham and Women's Hospital and colleagues collected data from 439 pregnant women enrolled in the Massachusetts General Hospital Obstetrical Maternal Study.

The information included homeostasis model assessment (HOMA) data, glucose load test (GLT) results, and clinical information including prepregnant body mass index (BMI), gestational weight gain, maternal age, delivery information, and infant birth weight.

All of the women had fasting blood samples drawn at 16–18 weeks gestation and all had GLT performed as part of routine care. Prepregnancy BMI was based on weight at first prenatal visit.

The investigators used multivariate analysis to predict infant birth weight as a function of the baseline characteristics of the study population and logistic regression to predict the odds of macrosomia and cesarean section, said Dr. Zera.

An analysis of the study population showed that 37% of the women in the study were overweight or obese prior to pregnancy, 17% of the infants in the cohort were macrosomic (more than 4,000 g), 27% of the deliveries were by cesarean section, and 30% of the cesarean deliveries were for macrosomia or failure to progress, Dr. Zera reported.

In the multivariate linear regression analysis, total gestational weight gain, prepregnancy BMI, and maternal age were significant predictors of birth weight, Dr. Zera said, noting that neither HOMA nor GLT were predictive. Both total weight gain and maternal BMI were significantly associated with risk of macrosomia in the logistical regression model, and maternal BMI alone was significantly associated with risk of cesarean section for macrosomia, she said.

Whereas glucose intolerance during pregnancy is thought to be a risk factor for macrosomia, the findings of this study suggest that “both maternal BMI and gestational weight gain may play more of a role than glucose intolerance in determining infant birth weight and subsequent risk of macrosomia and macrosomia-related cesarean delivery,” according to Dr. Zera.

Given these results, it is conceivable that reducing prepregnancy BMI and decreasing gestational weight gain may reduce the risk of macrosomia and subsequent cesarean delivery, Dr. Zera noted. As such, both should be emphasized clinically in women at risk, she said.

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