Metformin for Improving Maternal and Infant Outcomes in Pregnant Women Who Are Obese

Details for This Review

Study Population: Pregnant women who are obese (defined as first trimester or prepregnancy body mass index [BMI] of at least 30 kg per m²) who do not have preexisting diabetes mellitus or polycystic ovary syndrome

Efficacy End Points: Decrease in the risk that infants will be large for gestational age, defined as greater than 90th percentile for gestational age and sex

Harm End Points: Adverse events associated with medication, most notably diarrhea

Narrative: More than one-half of pregnant women in the United States are overweight or obese. Infants born to these women are at increased risk of prematurity, hypoglycemia, respiratory distress at birth, admission to the neonatal intensive care unit, stillbirth, congenital anomalies, macrosomia with possible birth injury, and childhood obesity. Overweight and obese women are also at increased risk of complications during pregnancy.1 Metformin, an inexpensive medication used to treat type 2 and gestational diabetes, improves insulin sensitivity by decreasing hepatic glucose production and increasing peripheral uptake and use of glucose. Women who are overweight or obese have increased insulin resistance, which exposes the developing fetus to higher levels of blood glucose over time and contributes to excessive fetal growth. Diet and lifestyle modifications have shown only modest effects in this population. Metformin use during pregnancy may increase insulin sensitivity, thereby decreasing the risk of maternal and fetal complications.2

A Cochrane review of three randomized controlled trials including 1,099 pregnant women in the United Kingdom and Alexandria, Egypt, compared metformin (initiation between 10 and 20 weeks' gestation and continuing