(579) Effect of metformin on basal insulin dose change in pregnant patients with type 1 diabetes

Type 1 diabetes mellitus (T1D) is primarily an insulin deficient state, but superimposed insulin resistance is increasingly seen. In the setting of pregnancy some patients can require high doses of insulin, and achieving euglycemia can be difficult. We have historically used metformin in such patients. The purpose of this study is to determine if the use of metformin in pregnant patients with T1D alters the rate of basal dose increase. 

Study Design:

A retrospective cohort study was conducted. Patients were included if they had T1D diagnosed prior to pregnancy, more than one documented prenatal visit with recorded basal insulin dose, and available delivery records. Demographic data included age, parity, hypertensive disorders, gestational age (GA) at delivery, mode and indication for delivery, birthweight, and NICU admission. T-test and chi square were used for demographic analysis. Basal insulin doses at initial prenatal visit, as well as 20, 24, 28, 32, and 36 weeks were collected. A difference-in-difference analysis was conducted in R to determine if basal insulin dose trend changed in patients prescribed metformin compared to those not prescribed metformin.

Results:

284 patients were eligible, of whom 29 were prescribed metformin. No difference was found between groups in age, parity, GA at delivery, mode or indication for delivery, hypertensive disorders, birthweight, or NICU admission. Starting basal insulin was 44u/d in metformin treated patients and 28u/d in non-treated patients (p< 0.01). Mean GA for starting metformin was 25 weeks. A difference-in-difference analysis using 25 weeks as the inflection point showed that metformin statistically significantly altered the trend of basal insulin dose compared to no medication (Figure 1, p=0.03).

Conclusion:

T1D patients prescribed metformin had higher baseline insulin requirements. Treatment was initiated at a mean GA of 25 weeks, significantly altering the trajectory for basal insulin dose. No differences in pregnancy outcomes were seen between patients who were treated with metformin and those who were not, suggesting safety of this intervention.