The prescribing information for metformin ER tablets states that limited data with the tablets in pregnant women are not sufficient to determine a drug-associated risk for major birth defects or miscarriage. For breastfeeding, it states there is insufficient information to determine the effects of metformin on the breastfed infant. This guide reports what the sources state and does not interpret them.
Pregnancy: what the label states
These statements come from the pregnancy subsection of the prescribing information for metformin ER tablets.
| Question | What the source says |
|---|---|
| What about the data in pregnant women? | Limited data with the tablets in pregnant women are not sufficient to determine a drug-associated risk for major birth defects or miscarriage. |
| What do published studies report? | Published studies with metformin use during pregnancy have not reported a clear association with metformin and major birth defect or miscarriage risk. |
| Can those studies rule out a risk? | The label states they cannot definitely establish the absence of any metformin-associated risk because of methodological limitations, including small sample size and inconsistent comparator groups. |
Breastfeeding: what the label states
The lactation subsection states that there is insufficient information to determine the effects of metformin on the breastfed infant and no available information on the effects of metformin on milk production.
Ovulation and unintended pregnancy
The label states to discuss the potential for unintended pregnancy with premenopausal women as therapy with the tablets may result in ovulation in some anovulatory women.
What the patient information says
The label also prints a patient information leaflet. Its pregnancy entry says it is not known if the tablets will harm your unborn baby, and that if you are pregnant you should talk with your healthcare provider about how to control your blood sugar while you are pregnant. Its breast-feeding entry says it is not known if metformin hydrochloride passes into your breast milk, and to talk with your healthcare provider about how to feed your baby while you take the tablets.
Two studies in groups of women
The label states the tablets are indicated as an adjunct to diet and exercise to improve glycemic control in adults with type 2 diabetes mellitus. The two studies below involved other groups of women, so use for those conditions is off-label.
A randomized trial in women with gestational diabetes mellitus compared metformin, with supplemental insulin if required, against insulin. It concluded that metformin is not associated with increased perinatal complications as compared with insulin. The abstract does not state the metformin dose.
A Cochrane systematic review of randomized trials in women with polycystic ovary syndrome (PCOS) undergoing ovulation induction reported that metformin versus placebo or no treatment may improve live birth rates (OR 1.59, 95% CI 1.00 to 2.51, 4 studies, 435 women). The evidence is described as low-quality. The abstract does not give a single metformin dose.
What this does not tell you
The label says the data are limited and cannot establish the absence of any risk. This guide does not turn that into a conclusion about risk or its absence. It also gives no counts of birth defects or miscarriages, because the label statements used here give none.
The ovulation statement says "may" and "some" and gives no figures here. The gestational diabetes trial compared metformin with insulin, not with placebo, and its finding is about perinatal complications. This guide does not list the complications, the group sizes or the dose.
This guide reports only the PCOS review's live birth finding, and the review describes that evidence as low-quality. Neither abstract states a single metformin dose. Other labels for metformin tablets are not covered here.
The patient information tells patients to talk with a healthcare provider in the situations listed above. A licensed provider decides about treatment during pregnancy, when planning a pregnancy, and during breastfeeding.