Maternal body mass index: a poor diagnostic test for detection of abnormal fetal growths.

We sought to determine if maternal body mass index (BMI; kg/m(2)) identifies newborns with abnormal fetal growth (small for gestational age [SGA], large for gestational age [LGA], or macrosomia) at >= 37 weeks. Singletons with reliable gestational age and without diabetes or hypertension were analyzed. Areas under the receiver-operating characteristic (AUC) curves were calculated for BMI (first visit, delivery, and the change during pregnancy) to identify abnormal growth. If the AUC was <= 0.75 then the diagnostic test was not useful. Among 3582 cohorts, SGA occurred in 10%, LGA in 9%, and 11% were macrosomic. AUC indicates that BMI at delivery is significantly better than BMI at first visit for identification of aberrant growth, but their AUCs were less than 0.75, indicating it is not a useful diagnostic test. Maternal BMIs (at first visit, delivery, or the change during pregnancy) are poor predictors of abnormal fetal growth.