Science You Can Use: Could taking metformin in pregnancy increase breastfeeding success of women with PCOS?

Hormonal causes of low milk supply are, in my mind, the final frontier of our understanding of milk supply problems.

We know a lot about the normal course of lactation in women without hormonal or metabolic imbalances, and how to protect and rebuild milk supply when one of many Booby Traps drives things off course.  But for those who do have hormonal imbalances and suffer milk supply problems, we know too little and have too few solutions to offer.

So I was very interested to see a new study published this year by a Norwegian research team investigating the effect of metformin use in pregnancy on breastfeeding outcomes among women with Polycystic Ovary Syndrome (PCOS).

PCOS, a hormonal imbalance affecting as many as 15% of all women, has for some time been implicated in milk supply problems.  But it’s a slippery issue – some women with PCOS have dramatic milk supply problems, some don’t, and some even have an oversupply.  The theory of its effect on lactation is that – in some cases – it may cause the underdevelopment of the breast during pregnancy (and possibly even in puberty), making less glandular tissue available for milk production and resulting in low milk supply.

One hope has been if that women took metformin, a drug which reduces PCOS symptoms, during pregnancy, they might be more likely to experience normal breast growth, setting them up to then develop a full milk supply.

The study published this year, an offshoot of a larger randomized trial (metformin vs. placebo), looked for associations between metformin use during pregnancy and 1) breast size growth, and 2) duration of breastfeeding among 186 women with PCOS.  It found:

There were no differences in the duration of exclusive breastfeeding or the duration of partial breastfeeding between mothers with PCOS treated with metformin and those treated with placebo.

There were no differences in breast size before pregnancy or breast size increment during pregnancy between the metformin and the placebo groups.

The duration of both exclusive and partial breastfeeding correlated positively with breast size increment in pregnancy.

Here are two other interesting findings:

Increased BMI (body mass index) [pre-pregnancy] was related to a shorter duration of breastfeeding.

Women with no breast size increment [growth] had higher blood pressure, were more obese, had higher fasting insulin and triglyceride levels already at inclusion in the first trimester of pregnancy, compared with those who experienced breast size increment.

I asked Lisa Marasco, IBCLC, author of The Breastfeeding Mother’s Guide to Making More Milk and expert on the hormonal causes of low milk production, for her comments (see my podcast interview with her on hormones and low milk supply).

She told me that her contention has been that metformin will help optimize breast development for breastfeeding, and that while this study didn’t confirm that, it may not have been a large enough sample.  She noted that she has seen a number of individual cases in which changes are reported.  She also noted two important findings:  1) women with PCOS who experience milk supply problems are likely more metabolically disturbed, and 2) women with fewer breast changes during pregnancy were more likely to have problems with milk production.

So this study’s results are disappointing, but they also raise many questions:  Did the women who had breast growth have it because they were taking metformin or because they were less meatoblically distrubed and were going to have normal breast growth anyway?  Would the women who were more metabolically disturbed have had breast growth if the dose had been higher?  Is it something about obesity (much more common among women with PCOS) which is causing milk supply problems?

And what if these moms had been taking metofrmin both in pregnancy and during lactation, instead of ending in pregnancy?  There are no studies of this beyond case reports.

Remember how I called the hormonal causes of low milk supply the final frontier?  For the estimated 15% of women who have PCOS, I’m grateful that this is an active area of research.

Do you have PCOS?  Did you have breast growth in pregnancy?  Did you take metformin ih pregnancy and/or lactation?  How has PCOS and/or metformin impacted your breastfeeding experience? 

Image credit:  Wikimedia Commons

5 thoughts on “Science You Can Use: Could taking metformin in pregnancy increase breastfeeding success of women with PCOS?

  1. I was diagnosed with PCOS at 19 I am now 30. I was on birth control etc.. for 11 years and I switched to the pill instead of nuvaring this past august and then I got a stomach bug and didn’t take the pill for 4 days and I got pregnant. FIrst surprise was that I got pregnant and yet I have PCOS and was told that when I wanted to have chidlren it might be difficult to get pregnant. So good news is I got pregnant even though it wasn’t planned. My question is that I never took metformin regularly before pregnancy and I am not taking it now. It made me sick and my glucose was always normal. Now that I am pregnant 25 weeks and reading this article I am concerned that not being on metformin I will have a low breast milk supply. SHould I discuss with my midwife and OB that I should go back on it and if I do would it make a difference this far a long in my pregnancy?


    1. Hi Laura Lee,

      You may want to check out The Breastfeeding Mother’s Guide to Making More Milk (West, Marasco), which has the most comprehensive discussion of PCOS and breastfeeding topic we know of.

      One of the authors just did a podcast on the topic which you can listen to here:

      Our best wishes for your pregnancy and breastfeeding!


  2. I was diagnosed with PCOS when I was 17, I am now 33. I was taking metformin regularly the last 6 years. I sought fertility treatments to get pregnant and was successful with clomid alone.the fertility specialist discontinued my metformin. When I became pregnant and was released to my OB she said it was up to me if I wanted to take it. Since I was using it only for weight loss (my BS stays WNL) I figured the less meds during pregnancy the better. Wish I had known about this study as now I am having a very hard time with a low milk supply. I get approx 1/2 oz per pump and need to supplement with formula. Any more updated info you may have would be great. I will be asking my GP if I can resume metformin at my next appointment.


  3. I have PCOS, pregnant 3 times trying not to get ptegnant, and BF each babe for 2-5 years. Interestingly, Instarted on metformin for blood sugar concerns and my milk supply (which was fine) amped up – much to my 8 month olds surprise!!


  4. I was diagnosed with PCOS at 19 and went on Levora/Noradette birth control pills to regulate my periods. When I got married at 32 my doctor switched me from birth control to metformin (750mg 2x/day) to help me get pregnant. After a year of no success I began Clomid, and got pregnant immediately. My progesterone levels were very low, but my doctor kept me on metformin and my pregnancy progressed even with the low numbers. I now have a beautiful 6-week old perfectly healthy girl (and I’m 34 now). I was instructed to stay on my metformin for the entire pregnancy to try to lessen my chances of gestational diabetes, and although my glucose was in the top of the average range the whole time, I did not get it. Once I gave birth I was told to STOP my metformin while breastfeeding. My breasts got larger during pregnancy (DD to F) and my milk cell in after birth, but after 6 weeks of easy feeding I can tell things are slowing down. I was researching ways to increase my supply, and came across this PCOS and breastfeeding link. None of my doctors ever mentioned this…should I still be taking metformin to keep my milk up? Does it effect the baby? I was so relieved to get pregnant and then keep it and have my wonderful girl that I didn’t know my stupid PCOS could still be messing me up in regards to her!


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