Taking Metformin During Pregnancy

Pregnant woman talking to a doctor who is holding a prescription bottle

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Metformin is a drug that is often prescribed, off-label, for the treatment of PCOS and for regulating ovulation. It belongs to a class of drugs that improves the cells' response to insulin and regulates blood sugar. An off-label prescription means that the FDA has not approved the use of a drug specifically for that condition. In this case, metformin has been approved for the treatment of diabetes but not for PCOS specifically.

How Metformin Works

Because so many women with PCOS also have insulin resistance and diabetes, it is believed that treating insulin dysfunction might have an effect on the other hormonal irregularities associated with the condition. While researchers aren’t sure of the exact mechanism, there is some evidence that backs up this theory: some studies have shown that women who take a combination of metformin and Clomid (a drug that is used to induce ovulation in anovulatory women) have a better response to the medication regimen than those who take Clomid alone. Some women with PCOS, especially those that are insulin resistant, may see more regular periods from taking metformin as well.


Dosages of between 1,500 mg to 2,000 mg daily are typical, depending on a woman's insulin resistance and risks of side effects. Many women taking metformin report having upset stomach, nausea and diarrhea — especially with higher doses. The doctor may recommend slowly increasing your dosage until you reach the prescribed dosage to increase your tolerance to the drug. Other physicians will recommend the extended-release form, meaning that a small amount of the medication is released throughout the day, instead of all at once like with a regular release pill. It is important to take your medication exactly as prescribed and let your doctor know if you are experiencing any side effects.

May 28, 2020: The Food and Drug Administration (FDA) has requested that manufacturers of certain formulations of metformin voluntarily withdraw the product from the market after the agency identified unacceptable levels of N-Nitrosodimethylamine (NDMA). Patients should continue taking their metformin as prescribed until their health professional is able to prescribe an alternative treatment, if applicable. Stopping metformin without a replacement can pose serious health risks to patients with type 2 diabetes.

Early Pregnancy Loss

In addition to difficulty becoming pregnant, women with PCOS may be at risk for pregnancy loss. This is due to an imbalance of hormones and higher levels of insulin. Several studies have shown a dramatically lower rate of pregnancy loss in women with PCOS taking metformin compared with women who were not taking metformin.

Gestational Diabetes

Unfortunately, women with PCOS are at a higher risk of developing gestational diabetes (diabetes in pregnancy). Research does support the use of metformin for reducing the risk for gestational diabetes in women with PCOS.

Safety in Early Pregnancy

Knowing that the drug may actually help protect you from pregnancy loss, the next question is often about safety. The studies are encouraging: so far, metformin has not been linked to any major birth defects or fetal malformations when taken during the first trimester. According to a study published in Human Reproduction, babies who were born to mothers who took metformin showed no differences in birth weight, length, growth, or motor-social development during the first 18 months of life compared with the normal US infant population.

If you are planning on becoming pregnant while taking metformin, make sure to talk to your doctor beforehand about what he or she wants you to do once you get a positive pregnancy test. Even though metformin is a category B drug, meaning that it is relatively safe in pregnancy, it is best to speak with your doctor and follow his instructions. Keep in mind, every doctor is different, and has their own plan for what is right for you and your baby.

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Article Sources
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  1. Lindsay RS, Loeken MR. Metformin use in pregnancy: promises and uncertaintiesDiabetologia. 2017;60(9):1612–1619. doi:10.1007/s00125-017-4351-y

  2. Hyer S, Balani J, Shehata H. Metformin in Pregnancy: Mechanisms and Clinical ApplicationsInt J Mol Sci. 2018;19(7):1954. Published 2018 Jul 4. doi:10.3390/ijms19071954

Additional Reading
  • Begum MR, Khanam NN, Quadir E, et al. Prevention of gestational diabetes mellitus by continuing metformin therapy throughout pregnancy in women with polycystic ovary syndrome. Journal Obstet Gynaecol Res. 2009;35(2):282-286.
  • Glueck CJ, Goldenberg N, Pranikoff J, Loftspring M, Sieve L, Wang P. Height, weight, and motor-social development during the first 18 months of life in 126 infants born to 109 mothers with polycystic ovary syndrome who conceived on and continued metformin through pregnancy. Human reprod. 2004;19(6):1323-1330.
  • Khattab S, Mohsen IA, Aboul Foutouh I, et al. Can metformin reduce glycaemic index diet in pregnancy to prevent macrosomia (ROLO study): randomised control trial. BMJ. 2012;345:e5605.
  • Kinnunen TI, Raitanen J, Aittasalo M, Luoto R. Preventing excessive gestational weight gain-a secondary analysis of a cluster-randomised controlled trial. Euro Clinical Nutr. 2012;66(12):1344-1350.
  • Kumar P, Khan K. Effects of metformin use in pregnant patients with polycystic ovary syndrome. J Human Reprod Sciences. 2012;5(2):166-169.
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