Intravenous glucose tolerance in pregnancy : maternal correlates and fetal outcome
To study maternal glucose tolerance in pregnancy and its effects on the fetus, a rapid 25g intravenous glucose tolerance test was performed at about 32 weeks gestation in a group of randomly selected women. Full glucose tolerance data was available in 815 cases. The results were withheld from the patients and their obstetricians and paediatricians, and no treatment or advice was offered. Fasting plasma glucose and indices of glucose disposal were distributed unimodally with no evidence of a separate pathological group towards the diabetic end of the distributions. Glucose disposal rate was not, however, signficantly associated with the fasting plasma glucose, suggesting that glucose intolerance associated with elevation of the fasting plasma glucose might be a more clearly defined entity. New reference standards for fasting plasma glucose in pregnancy, which differ from those currently in use, are presented. The major determinants of relatively impaired maternal glucose tolerance in pregnancy were maternal age and obesity. Nonetheless, many cases of relative glucose intolerance occurred in the absence of any preexisting clinical indication. Significant association were found between maternal glucose metabolism and various measures of neonatal size and morbidity, including the incidence of congenital malformations and the occurrence of perinatal asphyxia in post-term infants. These effects were graded through much of the range of maternal glucose tolerance and not of predictive value in individual cases. The available evidence did not indicate that these relationships were mediated by fetal hyperinsulinism. It is concluded that the adverse consequences of impaired glucose disposal with normal fasting plasma glucose in pregnancy do not justify exhaustive measures to identify the condition. Screening for glucose intolerance during pregnancy should seek to identify those cases in which glucose intolerance is associated with elevation of fasting plasma glucose.