Prevalence of nocturnal hypoglycemia in first trimester of pregnancy in patients with insulin treated diabetes mellitus

BACKGROUND: Excellent metabolic control before conception and during diabetic pregnancies is the aim in order to avoid malformations and perinatal morbidity. Since an inverse correlation between median blood glucose concentration (BG) and hypoglycemia as well as a high prevalence of nocturnal hypoglycemia have been described, we investigated the frequency of nocturnal hypoglycemia and the predictive value of bedtime blood glucose concentration for development of this condition in insulin treated diabetic patients. METHODS: During hospitalization, with no other changes in the patients' normal schedules, hourly blood samples were drawn from an iv-cannula from 22.00 h to 07.00 h for one night. BG (venous whole blood) and hemoglobin A1c were determined the following day. RESULTS: Fifty-three patients participated; subsequently ten were excluded due to discontinuation of blood sampling during the night, caused by either discomfort or cannula problems. Of the remaining 43 patients, 16 (37%) had at least one blood glucose <3.0 mmol/l. The duration of hypoglycemia was 2.4 (1-7) h with the highest prevalence at 05 h. Only one patient felt hypoglycemic during the night. Hemoglobin A1c was similar in patients with (7.1+/-1.2%, mean+/-s.d.) and without (6.8+/-0.8%) nocturnal hypoglycemia. Women with nocturnal hypoglycemia had significantly lower BG before bedtime compared to patients without hypoglycemia, 6.4+/-3.6 mmol/l vs. 7.9+/-2.4 mmol/l, p<0.05. The best predictive value for nocturnal hypoglycemia was a BG below 6.0 mmol/l at 23.00, which resulted in a risk of nocturnal hypoglycemia of 71%. Conversely, if the BG was > or =6.0 mmol/l, the chance of avoiding nocturnal hypoglycemia was 83%. CONCLUSION: Nocturnal hypoglycemia was seen with a prevalence of 37% during a night in the first trimester of pregnancy in insulin treated patients. Only one patient registered the hypoglycemia. Nocturnal hypoglycemia could be predicted in the majority of patients by measurements of BG before bedtime.