RELATION OF BIRTH-WEIGHT TO MATERNAL PLASMA-GLUCOSE AND INSULIN CONCENTRATIONS DURING NORMAL-PREGNANCY

Maternal diabetes mellitus is complicated by fetal macrosomia and pred isposes the offspring to diabetes, but recent evidence indicates that a low, not high, birthweight is associated with a higher incidence of Type 2 (non-insulin dependent) diabetes in adult life. To clarify the relationships between maternal glucose and insulin levels and birthwei ght, we measured oral glucose tolerance and neonatal weight in a large group (n = 529) of women during the 26th week of pregnancy. Women wit h gestational diabetes (n = 17) had more familial diabetes, higher pre -pregnancy body weight, and tended to have large-for-gestational-age b abies. In contrast, women with essential hypertension (n = 10) gave bi rth to significantly (p < 0.01) smaller babies. In the normal group (w ithout gestational diabetes or hypertension, n = 503), maternal body w eight before pregnancy and at term, maternal height, week of delivery, gender of the newborn, and parity were all significant, independent p redictors of birthweight, together explaining 23 % of the variability of neonatal weight. In addition, both fasting (p < 0.006) and 2-h post -glucose (p = 0.03) maternal plasma glucose concentrations were positi vely associated with birthweight independent of the other physiologica l determinants, accounting, however, for only 10% of the explained var iability. In a subgroup of 134 normal mothers with prepregnancy body m ass index of less than 25 kg . m-2, in whom plasma insulin measurement s were available, the insulin area-under-curve was inversely related t o birthweight (p < 0.02) after simultaneously adjusting for physiologi cal factors and glucose area. When glucose and insulin measurements we re combined in the I/G ratio (ratio of insulin to glucose area), this was still inversely related to birthweight. Furthermore, maternal insu linaemia was directly related to blood pressure levels (p < 0.001) ind ependently of body weight. We conclude that in normal pregnancy, where as physiological factors account for most of the explainable variabili ty of infant weight, the influence of the maternal metabolic milieu is dual, positive for glucose levels but negative for insulin concentrat ions. Maternal hyperinsulinaemia during pregnancy may be one trait lin king low birthweight with predisposition to diabetes in adult life.