Metformin use in pregnancy and impact on breastfeeding success

Metformin use is not linked to breastfeeding patterns in pregnant patients with type 2 or early diabetes, according to a recent study published in Pregnancy.¹

Risks of diabetes, hypertension, hyperlipidemia, and cardiovascular disease are reduced by breastfeeding, leading multiple organizations to recommend exclusive breastfeeding in the first 6 months of life and continued breastfeeding for at least the first 2 years.

Breastfeeding also reduces neonatal hypoglycemia and childhood diabetes risks in offspring of birthing parents with diabetes. However, these parents are less likely to breastfeed than their nondiabetic counterparts.²

“Finding effective ways to support breastfeeding success in pregnancies complicated by diabetes is critically important,” wrote investigators.¹

As insulin resistance has been linked to interference in successful breastfeeding upkeep, investigators hypothesized metformin as a potential treatment for improved breastfeeding. A secondary analysis was conducted to evaluate this association.

Participants included pregnant women aged 18 to 45 years with a single gestation diagnosed with type 2 or early diabetes. These patients were randomized 1:1 to receive either metformin or placebo.

Medical chart reviews were conducted to determine type 2 diabetes, while early pregnancy diabetes was determined based on 1-step testing, 2-step testing, glycated hemoglobin of 6.5% or more, capillary blood glucose of 126 mg/dL, or random capillary blood glucose of 200 mg/dL before 23 weeks’ gestation.

For the first week, participants took 500 mg metformin or matched placebo twice per day. After this period, the dosage was raised to 1000 mg twice per day if well tolerated.

Blood glucose was self-monitored by patients using a glucometer with a goal of 70 to 95 mg/dL fasting glucose in the morning and under 140 mg/dL for 1 hour postprandial and under 120 mg/dL for 2 hours postprandial.

Breastfeeding intentions were determined by a breastfeeding survey completed at 24- and 30-weeks’ gestation. Any breastfeeding during the postpartum hospital admission was considered immediate breastfeeding.

Further breastfeeding patterns were assessed through a phone call at 30 days postpartum. Additional questions were asked to patients who ceased breastfeeding to determine factors influencing breastfeeding success and the timing of cessation.

In the secondary analysis, patients delivering a live neonate, with at least 1 dose of the study drug, intention to breastfeed, and completing the breastfeeding surveys were included. Breastfeeding at 30 days postpartum was the primary outcomes, with other outcomes including immediate breastfeeding and lactogenesis onset.

There were 378 participants included in the final analysis, 194 of whom were in the metformin group and 184 were in the placebo group. Immediate postpartum responses were obtained from 80.9% and 78.3%, respectively, and 30-day postpartum survey responses from 62.4% and 65.2%, respectively.

Baseline breastfeeding intention scores did not differ between the 2 groups. There were also no differences observed in maternal age, body mass index, nulliparity, type of diabetes, hypertensive disorder, gestational ages at randomization and delivery, mode of delivery, neonatal birthweight, or neonatal intensive care unit admission.

Statistical significance was not found for breastfeeding rates at 30 days postpartum. Rates were 76% for the metformin group and 66.7% for the placebo group, indicating a difference of 9.3%. Additionally, exclusive and partial breastfeeding rates did not significantly differ.

Similar immediate breastfeeding rates were also reported between groups, at 91.1% in the metformin group and 88.9% in the placebo group. Formula supplementation during the postpartum period was reported by 87.9% and 93.1%, respectively.

Halting breastfeeding or primarily using formula was reported in 24.2% of the metformin group and 29.3% of the placebo group. No differences were reported in the week of breastfeeding cessation, and feeling like they achieved their breastfeeding goals at 30 days postpartum was reported in only 18.5% and 11.4%, respectively.

These results indicated prenatal metformin use is not associated with breastfeeding patterns among pregnant women with type 2 or early diabetes.

“Antepartum metformin should not be routinely prescribed to this population with the goal of improving breastfeeding success,” wrote investigators. “As the breastfeeding rates in the obstetric population with diabetes are typically low, future studies should focus on educational initiatives and methods to improve sustained breastfeeding in this population.

Reference:

1. Sarker M, Jacobs MB, Boggess K, et al. Breastfeeding patterns among parturients with diabetes: A secondary analysis of the MOMPOD randomized clinical trial. Pregnancy. 2025. doi:10.1002/pmf2.12040
2. Schoen S, Sichert-Hellert W, Hummel S, Ziegler AG, Kersting M. Breastfeeding duration in families with type 1 diabetes compared to non-affected families: results from BABYDIAB and DONALD studies in Germany. Breastfeed Med. 2008;3(3):171-5. doi:10.1089/bfm.2007.0027