DETERMINANTS OF BIRTH-WEIGHT IN WOMEN WITH ESTABLISHED AND GESTATIONAL DIABETES

Increased birth-weight (macrosomia) can complicate the diabetic pregna ncy, but many factors other than hyperglycaemia can influence birth-we ight, in particular maternal obesity. In a mixed population (European, Maori and Pacific Islander) with a high prevalence of glucose intoler ance and obesity we have examined the relative impact of various mater nal factors on birth-weight in women with both established and gestati onal diabetes. Mean birth-weight was significantly greater in women wi th established or gestational diabetes than in controls (p<0.0001), bu t was similar in women with gestational and established diabetes, desp ite glycaemic control being significantly poorer (p<0.0001) in the lat ter. Birth-weight closely paralleled prepregnancy body mass index rath er than glycaemic control, but in Maori women it was lower than expect ed, probably because of their high prevalence of smoking. Daily cigare tte consumption was negatively correlated with birth-weight (p<0.01) d espite the smokers having significantly poorer glycaemic control (p<0. 001). The most significant variables influencing birth-weight in the d iabetic pregnancy were gestational age at delivery, prepregnancy body mass index, maternal height, estimated weight gain during pregnancy, t he presence of hypertension and cigarette smoking (the latter 2 having negative effects on birth-weight). Glycaemic control in the last half of pregnancy was not significant in this analysis. We conclude that w ithin the limits of glycaemic control which we obtained, birth-weight was largely determined by maternal factors other than hyperglycaemia. Birth-weight thus has severe limitations as an outcome measure of the diabetic pregnancy.