Changes in medication initiation and selection patterns for gestational diabetes management

The reported frequency of medication management for gestational diabetes mellitus (GDM) varies widely in prior studies (8–56%) depending on study population and research approach.¹ Yet, recent trends in medication preference for GDM management remain understudied.¹ We examined changes in GDM medication use over time among Tennessee Medicaid (TennCare) recipients.

We identified pregnant patients with a diagnosis of GDM, aged 15–44 years, and enrolled in TennCare who delivered a live infant between 2007–2019 (Appendix A). Patients with type 1 and 2 diabetes, hypoglycemic medication prescriptions filled prior to GDM diagnosis, and GDM prescriptions filled for medications other than metformin, insulin, or glyburide were excluded. Data were derived from TennCare files linked to birth certificates and a statewide hospitalization registry. Filled prescriptions for GDM medications were used as a proxy for medication use. We identified the initial GDM medication filled after GDM diagnosis and used logistic regression to assess the association between delivery year and any GDM medication use accounting for maternal age, body mass index (BMI), race and ethnicity, residential distance from delivery facility, and facility. We also examined changes in use of specific GDM medications over time. The study was approved by our institution’s and the Tennessee Department of Health’s Institutional Review Boards, with exemption for informed consent given the large number of cohort patients and the retrospective nature of our study.

Among 32,177 pregnant patients with GDM included in the study, mean maternal age was 26.8 (±5.8) years and BMI was 30.3 (±8.4) kg/m² at delivery. Overall, 6,617 (20.6%) initiated pharmacotherapy for GDM with either metformin (34.9%), insulin (21.5%), or glyburide (43.6%). During the study period, we did not observe major changes in trends in maternal age, maternal pre-pregnancy BMI or the race/ethnicity composition of the study population (Appendix B and C). Substantial changes in selection of initial GDM medication were also observed over time. In 2007, most patients used glyburide (45.8%) or insulin (40.0%) and fewer used metformin (14.2%). Metformin use surpassed glyburide after 2016, with most patients receiving metformin in 2019 (63.2%) followed by insulin (27.5%) and glyburide (9.3%) (Figure). No relevant changes in TennCare medication formulary occurred during the study period.

Figure: Trends in initial GDM medication prescription (Glyburide, Metformin, or Insulin) by delivery year among pregnant Tennessee Medicaid patients with GDM, 2007 – 2019 (N=6,617).

*Delivery year significantly associated with increase in odds for medication initiation when adjusting for a priori selected variables including, maternal age (years), body mass index at delivery (BMI, kg/m²), race and ethnicity (White, Black, Hispanic, Asian, and other), distance from delivering facility (miles), and facility (p-value considered significant when p<0.05).

Orange short dash line: represents the American College of Obstetricians and Gynecologists guideline change (July 2017, reaffirmed in 2019) recommending that glyburide treatment should not be recommended as a first-choice pharmacologic treatment, over metformin or insulin.

Orange long dash line: represents the Society for Maternal Fetal Medicine guideline change (May 2018) recommending that both insulin and metformin are reasonable first-line options.

The prevalence of medication use among GDM patients in Tennessee Medicaid has increased over time, with metformin now the most commonly initiated GDM medication.

In a recent study of commercially insured beneficiaries, Venkatash et al. also observed substantial changes in GDM pharmacotherapies from 2015 to 2018, noting a shift from glyburide to insulin as the most common initial treatment for GDM.² In contrast, our study in a Medicaid population determined that metformin has replaced glyburide as the most used initial medication. Our data, from an underserved population enrolled in a Medicaid program, also differed with an overall lower use of insulin (21.5%) compared to metformin (34.9%) (Venkatesh et al’s study among privately insured patients: 31% vs 21%, respectively). These discrepant findings suggest possible differential prescribing based on socioeconomic status or regional differences in prescribing preferences. Publicly insured patients may also be preferentially prescribed oral hypoglycemic medications due to rising insulin costs. Nevertheless, the changes observed in our Medicaid study align temporally with emerging evidence on the safety and effectiveness of oral hypoglycemic medications^1,3,4 and corresponding changes in the American College of Obstetricians and Gynecologists (ACOG) practice recommendations,⁵ highlighting how practice patterns can shift quickly. Taken together, these studies underscore the need for additional assessments of factors that influence pharmacotherapy selection for GDM management, as well as the clinical impact of prescribing pattern changes on perinatal outcomes and healthcare costs.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.