OBJECTIVES -To investigate the frequency of severe hypoglycemia (SH) and hypoglycemic coma during the first trimester of type 1 diabetic pregnancy and in the 4 months before gestation and to identify risk indicators predicting first trimester SH in a nonselected nationwide cohort of pregnant women with type 1 diabetes.RESEARCH DESIGN AND METHODS -We conducted a longitudinal cohort survey in 278 pregnant type 1 diabetic women using questionnaires at inclusion and at 17 weeks of gestation, addressing the frequencies of SH (i.e., external help required) and hypoglycemic coma, general characteristics, hypoglycemia awareness, blood glucose symptom threshold, and the Hypoglycemia Fear Survey.RESULTS -The occurrence of SH (including hypoglycemic coma) rose from 0.9 Ϯ 2.4 episodes per 4 months before gestation to 2.6 Ϯ 6.3 episodes during the first trimester (P Ͻ 0.001), including an increase in episodes of coma from 0.3 Ϯ 1.3 to 0.7 Ϯ 3.7 (P ϭ 0.03). The proportion of women affected by SH rose from 25 to 41% (P Ͻ 0.001). First-trimester SH was independently related to a history of SH before gestation (odds ratio CONCLUSIONS -In type 1 diabetic pregnancy, the risk of SH is increased already before pregnancy and rises further during the first trimester. A history of SH before gestation, longer duration of diabetes, an HbA 1c level Յ6.5%, and a higher total daily insulin dose were risk indicators predictive for SH during the first trimester. Further research should aim to elucidate how the benefits of strict glycemic control balance with the markedly increased risk of SH early in pregnancy.[ Diabetes Care 25:554 -559, 2002

There is strong evidence that the avoidance of hyperglycemia is essential inoptimizing pregnancy outcome in type 1 diabetes. The price to pay is a striking increase in severe hypoglycemia (SH), defined as episodes requiring help from another person. During type 1 diabetic pregnancy, occurrence rates of SH up to 15 times higher as in the intensively treated group of the Diabetes Control and Complications Trial (DCCT) are reported. Blood glucose (BG) treatment targets differ considerably between clinics; some authors advocate lower limits as low as 3.3 mmol/l. Improved glycemic control and/or recurrent hypoglycemia (i.e. BG <3.9 mmol/l) may result in impairment of glucose counterregulatory responses. Also, glucose counterregulation may be altered by pregnancy itself. Short-acting insulin analogs may help reduce hypoglycemia with preservation of good glycemic control, but their use during pregnancy has yet to be proven safe.Several clinical studies did not establish an association between maternal hypoglycemia and diabetic embryopathy. However, animal studies clearly indicate that hypoglycemia is potentially teratogenic during organogenesis. Increased rates of macrosomia continue to be observed despite near normal HbA(1c) levels. This may, at least in part, be the result of rebound hyperglycemia elicited by hypoglycemia. Exposure to hypoglycemia in utero may have long-term effects on offspring including neuropsychological defects. It is yet unclear to what extent the benefits of tight glycemic control balance with the increased risk of (severe) hypoglycemia during type 1 diabetic pregnancy. Efforts must be made to avoid low BG, i.e. <3.9 mmol/l, when tightening glycemic control.

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