Magnetic Resonance Imaging in Pregnancies Complicated by Gestational Diabetes Predicts Infant Birthweight Ratio and Neonatal Morbidity

ABSTRACT

The use of magnetic resonance imaging (MRI) has been shown to be safe during pregnancy and can accurately assess fetal fat and rate of growth. The purpose of this study was to investigate with MRI the relationship between maternal weight, fat distribution, and glucose levels and neonatal birthweight ratio, percent fat, and infant outcome in pregnancies complicated by gestational diabetes. Twenty gestational diabetic women were studied at 36 to 38 weeks' gestation with hemoglobin A_1c, a glucose tolerance test and maternal body fat by electrical impedance. MRI scans of the maternal upper arm and from her zyphoid process to her pubic symphysis, including all fetal components, were analyzed for percent fat of the mother's arm and trunk and her fetus' trunk. All variables were then related to infant outcome (birthweight, birthweight ratio, and neonatal morbidity). Maternal body composition was related to maternal weight (p = 0.012, r = 0.54), as was maternal arm fat (p <0.005, r = 0.60). Arm fat did correlate with trunk fat, but trunk fat did not correlate was well with weight (p = NS). Although maternal Hb A_1c correlated with maternal weight (p = 0.05, r = 0.43), it did not correlate with infant birthweight. In contrast, maternal mean glucose levels correlated with both maternal and infant weight and infant birthweight ratio (p = 0.05, r = 0.60; p = 0.05, r = 0.42; and p = 0.01, r = 0.64, respectively). The infant birthweight ratio was predicted by the MRI, both by a subjective assessment of the images of fetal fat and by quantitating the fetal fat by determining the mean of two points of maximal fat thickness in the abdominal wall (p <0.001, r = 0.88). In addition, when the mother's arm was more than 50 mm² or the fetus was more than 4.0 mm mean thickness of maximal abdominal fat, the risk of macrosomia, and neonatal hypoglycemia increased. The MRI at 36 to 38 weeks of gestation is able to estimate birthweight ratio and neonatal morbidity in women with gestational diabetes.