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Evaluating Metformin Safety in Early Pregnancy for Type 2 Diabetes

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Within the realm of diabetes management, metformin stands as a cornerstone treatment for type 2 diabetes. However, the safety of its use during early pregnancy has been a topic of limited research. This study, leveraging data from the U.S. Medicaid health care administration database from 2000 to 2018, explores the teratogenic risks associated with metformin when used in the first trimester. By comparing outcomes between insulin monotherapy and a combination of insulin and metformin, researchers aimed to provide clearer insights into the potential risks for pregnant women with pregestational type 2 diabetes.

A comprehensive observational cohort study involving 12,489 pregnant women was conducted to assess the teratogenicity of metformin use during the first trimester. Participants were divided into two groups: 850 women received insulin monotherapy, while 1557 continued metformin and added insulin within 90 days of their last menstrual period (LMP).

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Study Design and Participant Details

The study emulated a target trial with two distinct treatment strategies: discontinuing metformin in favor of insulin monotherapy, and maintaining metformin alongside the initiation of insulin. This approach intended to evaluate the risks of nonlive births, live births with congenital malformations, and congenital malformations among live births.

Using standardization to adjust for covariates, researchers estimated the risk ratios and compared outcomes between the two groups. This detailed analysis aimed to provide robust evidence regarding the safety of metformin during early pregnancy.

Key Findings and Risk Analysis

The results demonstrated that the estimated risk for nonlive births was 32.7% in the insulin monotherapy group and 34.3% in the insulin plus metformin group, with a risk ratio of 1.02. For live births with congenital malformations, the estimated risk was 8.0% under insulin monotherapy and 5.7% for the insulin plus metformin group, yielding a risk ratio of 0.72.

These findings suggest that continuing metformin, while adding insulin during early pregnancy, poses little to no increased risk for nonlive births. The data were compatible with a range of outcomes, from a 49% decrease to a 9% increase in risk for congenital malformations under conventional statistical criteria.

User-Usable Inferences

– Insulin plus metformin strategy does not significantly increase the risk of nonlive births compared to insulin monotherapy.
– The combination therapy shows a potential decrease in the risk of congenital malformations among live births.
– Metformin continuation in early pregnancy might be a safer option than previously assumed for women with type 2 diabetes.

The study’s results highlight the importance of personalized treatment strategies for pregnant women with pregestational type 2 diabetes, emphasizing that metformin use does not significantly elevate risks when compared to solely switching to insulin therapy.

While the study opens promising avenues, further research is warranted to mitigate any residual confounding factors such as glycemic control and body mass index, which were acknowledged as limitations.

Original Article: Ann Intern Med. 2024 Jun 18. doi: 10.7326/M23-2038. Online ahead of print. PMID: 38885505 | DOI: 10.7326/M23-2038

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