Sandi Harris, Mercer University College of Pharmacy
According to a review of eight studies, research to evaluate the effects on both mother and fetus with the use of metformin in pregnant women who have been diagnosed with diabetes has shown some benefit. 
It has been stated that there is a positive correlation between maternal pre-pregnancy weight and gestational weight gain on the birth weight of the neonate. 
|Title: Metformin versus Placebo in Obese Pregnant Women without Diabetes Mellitus|
|Design||Double-blind, placebo-controlled trial; N= 400|
|Objective||To evaluate the effect on infant birth weight of metformin in women without diabetes who have a body mass index (BMI) of at least 35|
|Study Groups||Women receiving 3000 mg metformin daily during pregnancy (n= 202); Women receiving a placebo as a control group (n= 198)|
|Methods||The metformin or placebo was given with meals; metformin was initiated at a daily dose of 1.0 g in week 1, and the dose was increased by 0.5 g per week to a maximum dose of 3.0 g in week 5. Women with serious side effects while taking the full dose were asked to continue taking the maximum tolerated dose.|
|Duration||October, 2010 – June, 2015|
|Primary Outcome Measure||The median neonatal birth-weight z score (difference between observed and expected birth weight, with adjustment for gestational age, divided by the fitted standard deviation).|
|Baseline Characteristics||Metformin Group
|Maternal age, y||32.9||30.8|
|Results||Z-score= 0.05 in the metformin group [interquartile range, -0.71 to 0.92]; Z-score= 0.17 in the placebo group [interquartile range, -0.62 to 0.89] (p= 0.66)|
|Adverse Events||Common Adverse Events: N/A|
|Serious Adverse Events: Fetal growth restriction (1%)|
|Percentage that Discontinued due to Adverse Events: 17.6%|
|Study Author Conclusions||Among women without diabetes who had a BMI of more than 35, the antenatal administration of metformin reduced maternal weight gain but not neonatal birth weight|
This study shows that the birth weight of the baby was not affected when obese women who did not have diabetes received metformin during their pregnancy. Metformin may be an option to manage weight gain of the mother during pregnancy without negatively affecting the weight of the fetus.
- Zhu B, Zhang L, Fan YY, et al. Metformin versus insulin in gestational diabetes mellitus: a meta-analysis of randomized clinical trials. Ir J Med Sci. 2016.
- Santangeli L, Sattar N, Huda SS. Impact of maternal obesity on perinatal and childhood outcomes. Best Pract Res Clin Obstet Gynaecol. 2015;29(3):438-48.
- Syngelaki A, Nicolaides KH, Balani J, et al. Metformin versus Placebo in Obese Pregnant Women without Diabetes Mellitus. N Engl J Med. 2016;374(5):434-43.