Polycystic ovary syndrome (PCOS) and breastfeeding

Polycystic ovary syndrome (PCOS) and breastfeeding

We know that endocrinopathies can make breastfeeding difficult. Polycystic Ovary Syndrome (PCOS) is the most frequent endocrinopathy in women of childbearing age, with an incidence of between 6 and 10% of women. Together with other abnormalities, when PCOS is present, there is usually also insulin resistance, and therefore, there is a presence of hyperinsulinemia.

Women with Type 1 Diabetes Mellitus have a high incidence of PCOS and hyperandrogenism, and the use of external insulin may promote insulin resistance and weight gain.

It is known that individuals with these conditions tend to have more difficulties when initiating and maintaining breastfeeding. Evidence strongly suggests that despite having the same initial intentions and desire to breastfeed, breastfeeding rates in a population with pregestational diabetes 1 and 2 and PCOS are lower, and their breastfeeding durations are shorter.

Why is insulin resistance a problem?

The primary hormone involved in lactogenesis II (or milk let-down) is prolactin. However, other hormones such as cortisol, thyroxine, and oxytocin are also involved, and the role of insulin in this process is increasingly recognized.

In fact, delayed lactogenesis II can be predicted by markers of maternal metabolic health, and some studies suggest that better prenatal glucose tolerance, insulin secretion, and insulin sensitivity predict earlier lactogenesis in primiparous women who deliver full-term.

Among women with established Type 1 Diabetes Mellitus or pregestational Type 2 Diabetes Mellitus, it has been consistently observed that those with poor glycemic control have longer delays in lactogenesis than their peers with well-controlled diabetes.

In addition to a delay in the onset of lactogenesis, women with gestational metabolic disorders and insulin resistance are more likely to have persistently low milk production. (1)

Diagnosis of Polycystic Ovary Syndrome (PCOS)

A good diagnosis of PCOS needs to be carried out before reviewing the possible consequences of this condition on lactation. On many occasions, there is a population-wide confusion between having found some ovarian cysts during a scan and having one polycystic ovary and having the condition of polycystic ovarian syndrome.

The difference between these two circumstances needs to be explained correctly because they are entirely different from an etiopathogenic point of view.

According to the 2003 International Consensus Conference (2), a diagnosis of PCOS can be made if two or more of the following three characteristics are present:

  • Oligomenorrhea (infrequent or irregular menstrual periods)
  • clinical and/or biochemical hyperandrogenism
  • the presence of polycystic ovaries on ultrasound examinations

A diagnosis of PCOS should be made after excluding other disorders that may mimic PCOS, such as hyperprolactinemia, adult-onset congenital adrenal hyperplasia, Cushing’s syndrome, and androgen-secreting tumors. PCOS appears to have a hereditary component and is associated with candidate genes for insulin secretion and action and androgen synthesis and metabolism.


Metformin is a medication of the biguanide family, which helps to control blood glucose and decrease the absorption of free sugars from food. Therefore, it is used to improve PCOS endocrinopathy when trying to conceive during pregnancy and breastfeeding, and it is considered safe during all of these stages(3).

Effect of metformin on lactation

There are very few clinical trials that assess metformin to improve breastfeeding rates in women with PCOS.

In 2012, a trial was published in the second phase of the PregMet study (4); it was conducted in Norway and evaluated the impact of metformin on lactation in women who had PCOS according to the criteria mentioned above.

Two main variables were observed in this study: breastfeeding rates and duration of breastfeeding, as well as breast size increase before and during pregnancy.

No differences were observed in the duration of exclusive breastfeeding or the duration of partial breastfeeding between metformin-treated and placebo-treated mothers with PCOS.

There was also no difference in breast size increase before pregnancy or during pregnancy between the metformin- and placebo-treated groups.

It was observed that an increase in breast size was not related to maternal body mass index (BMI) or change in BMI.

The duration of exclusive and partial breastfeeding positively correlated with the increase in breast size during pregnancy.

A comparison was made between women who reported bra size increase during pregnancy and those who did not; women without bra size increase had higher blood pressure, BMI, and insulin and higher triglyceride levels when fasting.

Weight gain during pregnancy did not correlate with an increase in breast size when adjusting for baseline BMI. After childbirth, the women whose breasts did not increase in size had a shorter period of exclusive and partial breastfeeding.

Thus, women with PCOS who do not experience an increase in breast size during pregnancy appear to have more metabolic disturbances, and their lactation rates and durations are lower than those who do experience an increase in breast size. Metformin does not seem to change these results (4).

Much more research is needed on this topic to care for mothers with PCOS endocrinopathy adequately.



  1. Rassie, K., Mousa, A., Joham, A., & Teede, H. J. (2021). Metabolic Conditions Including Obesity, Diabetes, and Polycystic Ovary Syndrome: Implications for Breastfeeding and Breastmilk Composition. Seminars in reproductive medicine39(3-04), 111–132. https://doi.org/10.1055/s-0041-1732365
  1. Consensus. Revised 2003 consensus on diagnostic criteria and longterm health risks related to polycystic ovary syndrome (PCOS). Hum Reprod 2004;19:41–7.
  1. Glueck, C. J., & Wang, P. (2007). Metformin before and during pregnancy and lactation in polycystic ovary syndrome. Expert opinion on drug safety6(2), 191–198. https://doi.org/10.1517/14740338.6.2.191
  1. Vanky, E., Nordskar, J. J., Leithe, H., Hjorth-Hansen, A. K., Martinussen, M., & Carlsen, S. M. (2012). Breast size increment during pregnancy and breastfeeding in mothers with polycystic ovary syndrome: a follow-up study of a randomised controlled trial on metformin versus placebo. BJOG : an international journal of obstetrics and gynaecology119(11), 1403–1409. https://doi.org/10.1111/j.1471-0528.2012.03449.x

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