We analysed a database of glycosylated haemoglobin (HbA1) in nondiabetic pregnant women to investigate the relation between glucose metabolism in the first and second trimesters and hypertensive complications of pregnancy. From a total of 1334 women, 13 had pre-existing hypertension, 225 developed gestational hypertension and 51 developed pre-eclampsia. At 28 weeks of gestation, the women who susequently developed gestational hypertension had a significantly higher mean HbAl than those who remained normotensive (6.33 vs 6.17%, P < 0.02). This difference remained significant after correcting for the effects of age and body mass index (regression coefficient 0.11, SE 0.06, P = 0.05). In contrast, there were no significant differences in HbAl between the women with pre-eclampsia and their normotensive counterparts. This provides indirect evidence to support our hypothesis that gestational hypertension is associated with insulin resistance but pre-eclampsia is not.