Effect of maternal carbohydrate metabolism on fetal growth.

OBJECTIVE: To determine the effect of maternal carbohydrate metabolism and anthropometric characteristics on fetal growth. METHODS: Eight pregnant women in the third trimester with unexplained fetal growth restriction (FGR) and 11 women with normal pregnancies in the third trimester were evaluated for maternal carbohydrate metabolism, using oral glucose tolerance tests and hyperinsulinemic-euglycemic clamps. These data and maternal anthropometric characteristics subsequently were related to relative birth weight, defined as observed birth weight x 100/50th percentile birth weight. RESULTS: The women with FGR pregnancies were more insulin sensitive than were controls (21.6+/-4.4 versus 16.7+/-4.8 micromol/kg x min, P < .05) and showed reduced insulin and glucose areas under the curve (96,293+/-25,870 versus 145,291+/-49,356 pmol/L, P < .03; 1057.0+/-184.7 versus 1210.1 +/-85.9 mmol/L, P < .05, respectively). No differences were seen in fasting plasma glucose, insulin and human placental lactogen samples, age, height, pregravid weight, weight gain, and parity. In all patients, maternal insulin sensitivity and weight gain correlated well with relative birth weight (r =-.65, P < .002; r=.68, P < .001, respectively). When the same analysis was computed separately in the groups, insulin sensitivity exhibited a strong negative correlation with relative birth weight in the FGR group but not in controls (r=-.84, P < .007; r=-.54, P=.08, respectively). Conversely, in control women the best correlation between relative birth weight and the other variables studied was seen with maternal weight gain (r=.82, P < .002). CONCLUSION: Women with unexplained FGR have a different glucose metabolic pattern than do normals. We speculate that increased insulin sensitivity leads to a reduction in metabolic substrates for fetal growth.