Hi everyone, welcome to the LactFact weekly podcast, which highlights recent, clinically relevant research, policy statements, and protocols that you, as a practicing lactation professional, should know about. I am your host, Dr Anne Eglash. I am a board-certified family physician and breastfeeding and lactation medicine specialist at the University of Wisconsin School of Medicine and Public Health.

This podcast is written and produced by the nonprofit organization IABLE, which is the Institute for the Advancement of Breastfeeding and Lactation Education. There are no commercial funders for this podcast series.

Today’s Lactfact comes from the following article:
Breastfeeding patterns among parturients with diabetes: a secondary analysis of the MOMPOD randomized clinical trial
First author- Minhazur Sarker
Published – in the journal Pregnancy in January 2025

This study was done to determine if there is a relationship between taking metformin during pregnancy and breastfeeding initiation and continuation.

For background: It is pretty well established that people who are insulin resistant have a higher risk of delay in secretory activation and low milk production.

The authors cite evidence from animal studies that insulin treatment during pregnancy may have a positive impact on milk production.

The question here is whether improving insulin resistance with metformin during pregnancy will also help to increase milk production.

The researchers performed a secondary analysis of data that was collected in the MOMPOD study, which stands for Medical Optimization of Management of Overt Type 2 Diabetes in Pregnancy. That was a multicenter, double-blind, randomized controlled trial of metformin vs placebo, which were added to insulin to treat either pre existing type 2 diabetes or diabetes diagnosed during pregnancy. There were 831 pregnant subjects in this study, and the dose of metformin was 1000mg twice a day.

Of the 831 subjects 468 filled out a breastfeeding intention survey, and they included breastfeeding data on the 385 pregnant subjects who intended to breastfeed.

They measured whether the subjects were breastfeeding in the first 3 days, and again at 30 days postpartum.
The metformin vs placebo groups were very similar demographically, with no difference in the % who intended to breastfeed.

Here’s what they found:
There was no significant difference between the metformin and placebo groups regarding the % who initiated breastfeeding.
There was also no difference in the timing of secretory activation. Both groups had high formula supplementation at some point, 87.9% in the metformin group and 93.1% in the placebo group, with this difference not being significant.
At 30 days postpartum 76% of those in the metformin group were breastfeeding vs 66.7% in the placebo group, and that difference was also not significant. There was no difference between the groups regarding exclusive vs partial breastfeeding. In both groups, around 58% of participants felt that maternal milk production was a very important factor in breastfeeding success.
The authors concluded that taking metformin during pregnancy has not been shown to increase milk production, and so therefore should not be prescribed during pregnancy for that reason.

Here are my thoughts.
I think a major limitation of this study is that breastfeeding rates postpartum are not necessarily markers of volume of milk production, which was not measured. So it is a stretch to assume that the breastfeeding rates reflected milk production.

Approximately half of the subjects in the placebo and metformin groups were on medical assistance, which would be associated with socioeconomic and employment challenges to breastfeeding, thereby having major impacts on breastfeeding rates. They also cited the many challenges that pregnant individuals with diabetes have, such as a higher risk of cesarean birth, hypertension, elevated BMI, NICU admission and neonatal delivery complications, all of which can also impact breastfeeding rates.

Based on my clinical experience, I am aligned with their conclusion, though, that metformin during pregnancy will not likely impact milk production, even though they made this conclusion in an indirect way since they didn’t measure milk volumes. Clinically, I have never seen an impact of metformin during pregnancy on milk production.

This study didn't document the percent of women who continued to take metformin after delivery because the protocol deferred postpartum diabetes management to the health care provider.

I would say, though, that among my patients with insulin resistance, metformin and/or goats rue immediately postpartum appear to increase milk production faster in the first several weeks compared to those who don’t take a galactagogue that can reduce insulin resistance. I notice that the increase in milk production tends to be slow but steady, often increasing approximately 30ml/week, and sometimes faster. The authors touched on the research done using metformin postpartum and cited 2 very small studies that were not powered sufficiently to identify a difference in milk production among those taking metformin versus placebo.

I am going to conclude by saying that we need larger and well-controlled studies on the relationship between milk production and the use of galactagogues that improve pre-pregnancy and pregnancy-induced insulin resistance. I believe this is really where we can have the greatest impact for women at risk for low milk production.

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I will talk to you again in 2 weeks!