Metformin & Pregnancy: What to Know

Key Takeaways

Research suggests that metformin is generally safe for pregnant women with Type 2 diabetes. While there are no adequate human studies, animal studies have not shown any risk to the unborn baby.
If lifestyle modifications alone are not adequate to lower blood glucose, insulin is the first-choice medication for all types of diabetes in pregnant women.
Traditionally, metformin is the first go-to medication for everyone with a new Type 2 diabetes diagnosis. Notably, metformin is also commonly used as off-label treatment for gestational diabetes.

Metformin is one of the most commonly prescribed oral hypoglycaemic agents to control high blood sugar levels in people with Type 2 diabetes mellitus. Research suggests that metformin is generally safe for pregnant women with type 2 diabetes. It can also be used to treat women with gestational diabetes mellitus (diabetes that develops during pregnancy). Metformin is also prescribed off-label to treat polycystic ovarian syndrome (PCOS). Please continue reading to find out how metformin affects pregnancy outcomes.

Is metformin safe while pregnant?

Metformin is a pregnancy category B drug, meaning there are no adequate human studies, but animal studies have not shown any risk to the unborn baby.

Systematic review and meta-analysis suggest that metformin administration during pregnancy is not associated with an increased risk of pregnancy complications, pregnancy loss, or congenital anomalies (birth defects) in the baby. However, metformin crosses the placenta, and therefore, when pregnant women take this drug, the baby is exposed to it as well.

As mentioned, insulin is considered the first-line therapy for all types of diabetes during pregnancy, according to the American Diabetes Association.

Studies comparing metformin versus placebo in pregnant women with Type 2 diabetes mellitus have shown the following maternal and neonatal outcomes:

Compared to women in the placebo group, women treated with metformin during pregnancy achieved better glycemic control (lower HbA1C and average blood glucose readings), required less insulin, and had less gestational weight gain.
Compared to babies in the placebo group, infants exposed to metformin weighed less with a lower average birth weight and had lower adiposity measures.

Notably, these clinical trials were conducted on pregnant women who already have Type 2 diabetes, and women with gestational diabetes were not included in these trials.

Metformin versus insulin: Which is better in pregnancy?

Insulin is typically used to treat pregnant women with Type 2 diabetes mellitus that is not controlled with healthy lifestyle measures. Metformin is the preferred first-line treatment for type 2 diabetes in non-pregnant individuals.

Studies in women with gestational diabetes mellitus treated with metformin versus insulin have shown the following maternal and infant outcomes in the metformin group:

Lower incidence of hypoglycemia (low blood sugar).
Lower incidence of newborns who are small for gestational age.
Lower rates of prematurity, neonatal jaundice, and NICU (neonatal intensive care units) admissions.
Less maternal obesity as metformin reduces weight gain in obese pregnant women.
Lower risk of large birth weights, which helps reduce the risk of complications during delivery.

Individual responses may vary. The decision between metformin and insulin should be based on a thorough assessment of the pregnant woman’s medical history, glucose control, and other factors.

Are there any risks associated with taking metformin during pregnancy?

Taking metformin during pregnancy may be associated with:

A higher rate of induced labor or planned cesarean sections (C-sections)
Low birth weight in infants

The good news is a large study conducted on children whose mothers take metformin during pregnancy found that these children are not at increased risk of long-term complications, including obesity, abnormal blood sugar, and other developmental issues.

Can metformin be used to treat gestational diabetes mellitus?

Diabetes in pregnancy (gestational diabetes) is associated with an increased risk of poor maternal and fetal outcomes. If dietary and lifestyle advice is not successful in controlling blood glucose levels, doctors frequently use insulin for treating gestational diabetes mellitus.

However, a double blind placebo controlled trial called the Metformin in Gestational Diabetes (MiG) RCT found that metformin use during pregnancy has similar outcomes to insulin for the treatment of gestational diabetes but with less maternal weight gain and greater patient acceptability (metformin is an oral medication taken by mouth while insulin must be injected).

Keep in mind that while metformin is commonly used as an off-label treatment for gestational diabetes, your healthcare provider will choose the best medication, insulin versus metformin, for you.

Can metformin help with fertility problems in polycystic ovary syndrome?

Clinical trials have shown that metformin treatment can have beneficial effects on reproductive abnormalities in women with polycystic ovary syndrome (PCOS). The use of metformin can increase insulin sensitivity and help restore ovulation, cure infertility, prevent pregnancy loss, and reduce pregnancy complications such as gestational diabetes mellitus, preeclampsia, and preterm labor, which are linked to insulin resistance in PCOS. Metformin is not a fertility treatment but may improve ovulation and menstrual regularity, contributing to improved fertility in some cases.

Does metformin have any effects on labor?

Research on metformin has shown that children of women taking metformin during pregnancy are not at increased risk for birth defects. However, women taking metformin during pregnancy are more likely to have an induced labor or planned cesarean section.

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