Objective: To assess the relationship between glycemic control, pre-eclampsia, and gestational hypertension in women with type 1 diabetes.

Research design and methods: Pregnancy outcome (pre-eclampsia or gestational hypertension) was assessed prospectively in 749 women from the randomized controlled Diabetes and Pre-eclampsia Intervention Trial (DAPIT). HbA(1c) (A1C) values were available up to 6 months before pregnancy (n = 542), at the first antenatal visit (median 9 weeks) (n = 721), at 26 weeks' gestation (n = 592), and at 34 weeks' gestation (n = 519) and were categorized as optimal (<6.1%: referent), good (6.1-6.9%), moderate (7.0-7.9%), and poor (≥8.0%) glycemic control, respectively.

Results: Pre-eclampsia and gestational hypertension developed in 17 and 11% of pregnancies, respectively. Women who developed pre-eclampsia had significantly higher A1C values before and during pregnancy compared with women who did not develop pre-eclampsia (P < 0.05, respectively). In early pregnancy, A1C ≥ 8.0% was associated with a significantly increased risk of pre-eclampsia (odds ratio 3.68 [95% CI 1.17-11.6]) compared with optimal control. At 26 weeks' gestation, A1C values ≥ 6.1% (good: 2.09 [1.03-4.21]; moderate: 3.20 [1.47-7.00]; and poor: 3.81 [1.30-11.1]) and at 34 weeks' gestation A1C values ≥ 7.0% (moderate: 3.27 [1.31-8.20] and poor: 8.01 [2.04-31.5]) significantly increased the risk of pre-eclampsia compared with optimal control. The adjusted odds ratios for pre-eclampsia for each 1% decrement in A1C before pregnancy, at the first antenatal visit, at 26 weeks' gestation, and at 34 weeks' gestation were 0.88 (0.75-1.03), 0.75 (0.64-0.88), 0.57 (0.42-0.78), and 0.47 (0.31-0.70), respectively. Glycemic control was not significantly associated with gestational hypertension.

Conclusions: Women who developed pre-eclampsia had significantly higher A1C values before and during pregnancy. These data suggest that optimal glycemic control both early and throughout pregnancy may reduce the risk of pre-eclampsia in women with type 1 diabetes.