The ranges of insulin response and glucose tolerance in lean, normal, and obese women during pregnancy.

We characterized insulin secretion and glucose disposal in a large unselected group of women, encompassing the full spectrum of glucose tolerance in pregnancy, and related the findings to maternal obesity. Intravenous glucose tolerance and first-phase insulin response were measured at about 32 weeks' gestation in 690 unselected pregnancies. The women were designated as "lean," "normal," or "obese" on weight-for-height criteria. The distribution of insulin response was bimodal, but there was no corresponding dichotomy in maternal glucose disposal rate. Insulin response was greatest and glucose disposal rate slowest in obese women. In general, "poor" glucose tolerance was associated with relatively low insulin output. It was not possible to identify any cluster of women, obese or otherwise, in whom poor glucose tolerance was specifically associated with an unusually high insulin response. The data indicate that the distribution of glucose tolerance in pregnancy is a continuum. Glucose intolerance represents one end of that spectrum and is attributable to insufficient insulin secretion. This relative insufficiency is most frequent with maternal obesity.