What’s going on with your thyroid function during pregnancy & how does it affect your breastmilk supply?

What’s going on with your thyroid function during pregnancy & how does it affect your breastmilk supply?

As many know, pregnancy and breastfeeding come with a lot of important physiological and hormonal changes in a woman’s body. Some of these hormonal changes can also mess up your thyroid function, causing an increase or decrease in thyroid hormones even in women who have never had thyroid issues before.


Hypothyroidism is a health condition in which the thyroid gland does not make enough thyroid hormone to regulate your metabolism. If your thyroid gland can’t secrete adequate amounts of hormones into your bloodstream, your body’s metabolism slows down rapidly, resulting in symptoms like weight gain, fatigue, hair loss, dry skin, alteration in cognition, infertility, and menstrual abnormalities. (R, R)

Hypothyroidism is the most common thyroid disorder in Australia and mainly affects women above the age of 40. It is believed to affect around 6 – 10 % of women. The most common cause of hypothyroidism in Australia is Hashimoto’s disease, or thyroiditis, which is an autoimmune disease, occurring when the body’s immune cells attack the thyroid gland. (R, R)

Thyroid diseases include not only hypothyroidism, but also hyperthyroidism which is an over-active thyroid, and thyroid cancer. There is also a condition called postpartum thyroiditis which can occur during the first year after delivery; it may present as hypothyroidism alone, hyperthyroidism alone, or hyperthyroidism followed by hypothyroidism. (R)


Thyroid problems are common in pregnancy. This is because the hormonal and metabolic changes that take place during this stage also lead to profound alterations of the biochemical parameters of the thyroid function. Iodine also plays a key role during both, pregnancy and lactation, and its deficiency has been linked with thyroid disorders. (R)

If the thyroid gland doesn’t work well during gestation, it can affect the mother’s health as well as the child’s, before and after delivery. These problems include miscarriage, intrauterine growth restriction, preterm birth, low birth weight, perinatal mortality and pre-eclampsia. (R)

More importantly, thyroid hormones are critical for the growth and proper development of your baby’s brain; for example, it has been suggested that a low thyroid function can have harmful effects and alter the neuro-intellectual development in the early life of the child. So, if hypothyroidism in the mother is not treated promptly, it can lead to impaired brain development in the baby, increasing the risk of mental retardation. (R)

Likewise,  children of mothers with severe iodine deficiency during pregnancy can have intellectual disabilities and problems with growth, hearing, and speech. Cretinism, though rare nowadays, is the most severe form of an underactive thyroid, and it is characterized by permanent brain damage, deaf mutism, spasticity, and short stature. (R)

But please, don’t panic! Because hypothyroidism is possible during your pregnancy, clinicians recommend that pregnant mothers should assess their thyroid function and check thyroid levels before and throughout the gestation period.

As I mentioned before, hormonal changes during pregnancy alter thyroid function, this means that lab tests of thyroid function also change and must be interpreted carefully while being pregnant. If the TSH, Free T4 and Free T3 levels are within the normal range, your thyroid is functioning normally.  And those who have thyroid dysfunction should get appropriate treatment and follow up until their thyroid function is restored and normal again. (R)


Thyroid problems can also appear during breastfeeding, even in women who have never had thyroid problems before. As I mentioned at the beginning, postpartum thyroiditis can present during the first postpartum year in several forms, but the most common presentation is hypothyroidism without preceding hyperthyroidism. (R) For me personally, I had had hypothyroidism for a long time, but never thought to really monitor it during pregnancy, nor realised how much it could affect my breastmilk supply with my child. I wish I had connected the dots earlier! Read here about my personal struggles with low breastmilk supply and thyroid disease.


During breastfeeding, thyroid hormones are involved in normal breast development and also help in breast milk production. So, when inadequate thyroid hormones are made, some mothers will struggle to make adequate breast milk. This can make your baby gain weight slowly or not gain at all.

Many studies have reported that milk supply is sensitive to the level of thyroid hormones in the bloodstream. Some women reported that when their thyroid hormone levels were out of the normal range, they were not able to support full milk production. However, if replacement therapy was adequate, the relief of the symptoms and an increase in breast milk supply was seen.

Women who have thyroid issues and want to increase their milk supply, might be willing to use galactogogues to increase the milk supply, however, you should be aware that fenugreek consumption can actually make thyroid problems worse and do the contrary, by reducing milk supply.

Usually women diagnosed with hypothyroidism are treated with thyroxine in order to bring the levels back to normal. You don’t need to worry about medical treatment, as it’s perfectly safe and compatible with human milk and has no adverse effect on the baby either. (R)


Yes! It is well known that higher blood levels of thyroid stimulating hormone (TSH) and lower levels of free thyroxine are linked with higher body weight and body mass index. Women with higher TSH levels are at an increased risk of gaining excess weight during pregnancy, and they are more likely to have had a higher pre-pregnancy weight or BMI (Body Mass Index). (R, R)

But, is being overweight your destiny if you suffer from hypothyroidism? Not at all! As I explained before, thyroxine mimics the function of the hormones that are naturally produced by the thyroid gland. So if you get adequate thyroxine replacement, it should raise your metabolic rate again and ease hypothyroidism symptoms, including weight issues.

You can also help yourself by exercising regularly. Physical activity can increase your muscle mass as well as your metabolic rate. Besides, exercise can help you feel better and it’s considered a natural antidote to symptoms such as depression and low energy levels. Other research has suggested that regular aerobic exercise stimulates thyroid gland secretion and can boost hormone production in the thyroid and thus, improve TSH levels. (R) (R)

You should also visit an Accredited Practicing Dietitian to follow an individualised meal plan according to your postpartum needs, ensuring your diet is meeting your high nutrient needs during this time, particularly if you are breastfeeding as weight loss can affect breastmilk supply. In summary, following a good diet plan and exercising are excellent ways to achieve and maintain weight loss for someone with hypothyroidism. (R, R)

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