Metformin in GDM: Anchoring Glycemic Control with Maternal and Fetal Safety - Dr Shalini Jaggi

Gestational Diabetes Mellitus (GDM) is a growing public health emergency, particularly in India where prevalence ranges from 3.8% to 21% (1). Characterized by glucose intolerance first recognized during pregnancy, GDM elevates risks for both mother and child, including preeclampsia, macrosomia, and neonatal metabolic distress. In the light of the evolving evidence landscape, metformin is gaining relevance as a safe, beneficial, oral, convenient, and affordable treatment option, with emerging research supporting its anchoring role in individualized glycemic management of GDM (2).

Metformin Anchoring Potential in GDM: What is the Mechanistic Rationale?

Metformin, a biguanide, acts as an insulin sensitizer by reducing hepatic glucose production and increasing peripheral glucose uptake (2). It reduces fasting serum insulin by 40% and leads to a mean weight reduction of 5.8%. Metformin also stimulates glucagon-like-peptide-1 (GLP-1) release thereby enhancing insulin secretion (3).

Clinical Efficacy of Metformin in GDM Women: What is the Recent Evidence?

Recent clinical evidence, particularly from the Indian subcontinent, underscores metformin’s efficacy and safety in GDM:

1. A 2026 retrospective analysis conducted at a tertiary care centre evaluated 278 women with GDM and reported more stable glycaemic control with metformin than insulin. Women receiving metformin had a significantly lower mean HbA1c compared with those treated with insulin (5.3 ± 0.7% vs 6.2 ± 1.8%; p < 0.001). A "birth weight paradox" was observed where infants in the metformin group were healthier on average (3496 g vs. 3348 g). This was not a result of overgrowth, but was directly linked to a markedly lower rate of prematurity (4.0% vs. 19.5%) compared to the insulin-managed cohort. These findings suggest that metformin is not merely an alternative to insulin, but may offer significant protective advantages against iatrogenic prematurity and neonatal metabolic distress in GDM women (4).

2. In a 2025 prospective observational study involving 60 pregnant women, fasting blood glucose was significantly lower among women treated with metformin compared with those receiving insulin (102.4 ± 9.1 mg/dL vs 109.2 ± 10.6 mg/dL). Neonatal hypoglycaemia was more commonly seen in the insulin group (40.0%) as compared to metformin group (23.3%) although this difference was not statistically significant (p = 0.266). Metformin showed better treatment compliance and was associated with fewer adverse neonatal outcomes. The authors concluded that metformin may serve as a practical first-line pharmacological alternative in GDM, particularly in resource-limited settings where oral therapy, affordability and adherence are important considerations (2).

3. In a South Indian randomized non-inferiority trial, 44 women with GDM received either metformin or insulin and were assessed using continuous glucose monitoring. Both groups showed comparable CGM outcomes, with no significant differences in time-in-range, time above or below range, mean glucose, or glucose management indicator, supporting metformin as an acceptable oral option in this patient population. The study further noted that metformin’s oral administration offers advantages such as improved patient compliance and acceptance in women with GDM, supporting its role as an acceptable oral option in this patient population (5).

Metformin: Emerging Insights on Maternal Benefits & Safety Profile

Metformin therapy is associated with lower maternal weight gain (a mean reduction of 1.57 kg compared to insulin) and a potential 31% reduction in the risk of preeclampsia (4). It has been validated for maternal efficacy and safety, achieving comparable glycemic control compared with insulin. Additionally, it reduces maternal weight gain and possibly the occurrence of hypertensive disorders (6). From a postpartum perspective, metformin may also be continued during breastfeeding when clinically appropriate, as only minimal amounts pass into breast milk and no adverse effects have been reported in breastfed infants (7).

Figure 1. Anchoring Potential of Metformin in GDM

Metformin Use in GDM: What are the Fetal-Neonatal Benefits & Safety Considerations?

Maternal metformin treatment increases fetal brain Sirtuin-1, a change that is beneficial for the developing fetal brain through support of neuronal differentiation and prevention of mitochondrial loss. Lower Sirtuin-1 may contribute to cognitive impairments and reduced brain plasticity (8). In a randomized clinical trial, metformin was found to be a safe and effective strategy for reducing betamethasone-induced maternal hyperglycaemia and neonatal hypoglycaemia. These findings suggest that metformin may also be considered in women receiving antenatal corticosteroids to mitigate steroid-related dysglycemia and associated neonatal risks (9).

Metformin in GDM: What are the Key Points from Regulatory & Guidelines Recommendations?

Metformin in GDM – Quick Take in 2026

Expert Perspective

In clinical practice, the decision to use metformin in GDM needs to be guided by the woman’s glycemic pattern, gestational age, renal status, and obstetric risk profile. For appropriate candidates, metformin offers a pragmatic treatment option, particularly where early pharmacological intervention is needed, but injectable therapy may affect adherence. However, treatment response must be reviewed closely, and insulin should be added without delay when glycemic targets are not achieved.

Practice Takeaways

• Metformin consideration in GDM needs to be followed with a structured clinical assessment of fasting/postprandial glucose pattern, gestational age, renal status, gastrointestinal tolerance, fetal growth profile and the woman’s ability to adhere to treatment and follow-up monitoring.
• With emerging evidence supporting maternal glycemic stability, lower maternal weight gain, and reassuring fetal–neonatal outcomes, metformin may serve as an oral treatment option anchoring individualized GDM care.

Abbreviations:

HbA1c: Glycated hemoglobin, mg/dL: Milligrams per deciliter, CGM: Continuous glucose monitoring, CDSCO: Central Drugs Standard Control Organization, SR: Sustained release, FOGSI: Federation of Obstetric and Gynaecological Societies of India, NICE: National Institute for Health and Care Excellence, UK: United Kingdom, DIPSI: Diabetes in Pregnancy Study Group India