Declining insulin requirement in the late first trimester of diabetic pregnancy

OBJECTIVE - To investigate whether pregnancies complicated by type 1 diabet es are associated with a decrease in first-trimester insulin requirement. R ESEARCH DESIGN AND METHODS - We examined the weekly insulin requirement (as units p er kilogram per day) during the first trimester of pregnancy in diabetic wo men in the Diabetes in Early Pregnancy Study (DIEP) viith accurate gestatio nal dating, regular glucose monitoring, daily insulin-dose recording, and m onthly glycohemoglobin measurements. RESULTS - In pregnancies that resulted in live-born full-term singleton inf ants, a significant 18% increase in mean weekly dosage was observed between weeks 3 and 7 (P = 0.000), followed by a significant 9% decline from week 7 through week 15 (P = 0.000). Further testing localized a significant chan ge in insulin dose in the interval beginning weeks 7-8 and ending weeks 11- 12 (P = 0.014). Within this interval, the maximum decrease was between week s 9 and 10 (mean), 10 and Il (median), and 8 and 9 (most frequent maximal d ecrease). To determine whether prior poor glucose control exaggerated these trends, we categorized the women based on their glycohemoglobin values: <2 SDs above the mean of a normal population (subgroup 1), 2-4 SDs (subgroup 2), and >4 SDs (subgroup 3) at baseline. Late first-trimester declines in d osage were statistically significant in subgroup 2 (P = 0.002) and subgroup s 2 and 3 together (P = 0.003). Similarly, women with BMI > 27.0 had a grea ter initial insulin rise and then fall compared with leaner women. CONCLUSIONS - Observations in the DIEP cohort disclose a mid-first-trimeste r decline in insulin requirement in type 1 diabetic pregnant women. Possibl e explanations include over-insulinization of previously poorly controlled diabetes, a transient decline in progesterone secretion during the late fir st-trimester luteo-placental shift in progesterone secretion, or other horm onal shifts. Clinicians should anticipate a clinically meaningful reduction in insulin requirement in the 5-week interval between weeks 7 and 12 of ge station.