Thyroid hormones interact with a woman’s reproductive hormones. A normal thyroid function is essential for ovulation, egg implantation and maintenance of a healthy pregnancy.¹

Menstruation and fertility

The right amount of thyroid hormone is necessary for normal function of the ovaries. Too much or too little of these hormones can cause menstrual disturbances and adversely impact fertility.¹

Women with hyperthyroidism usually experience very light menstrual blood flow and more frequent periods (less than 21 days in between). On the other hand, women with hypothyroidism tend to have heavy and prolonged menstruation.¹

An undiagnosed thyroid condition can make it difficult to conceive. Get your thyroid gland checked if:

• You have been trying unsuccessfully to get pregnant for more than 12 months²
• You have had two or more miscarriages²
• You have abnormal or irregular menses ²
• You have polycystic ovary syndrome (PCOS)^2,3‍

PCOS is a condition that affects how a woman's ovaries work, resulting in female to male hormone imbalance. Normally, women make small amounts of male hormones (called androgens), such as testosterone, but women with PCOS produce slightly higher amounts.⁵ It is particularly important to have your thyroid checked if you suffer from PCOS, as you are more likely to have problems with your thyroid function if you have these conditions.³

Correcting the underlying cause of hyperthyroidism or hypothyroidism should reverse menstrual abnormalities and thus improve fertility.³

Pregnancy

Pregnancy causes several physiological and hormonal changes that impact the thyroid gland and may lead to increased thyroid hormone requirements. The baby is also dependent on the mother for its supply of thyroid hormones during pregnancy, especially in the first trimester if the foetal thyroid is not yet functional.⁶

It is essential that your thyroid gland is functioning properly during this critical period, and expectant mothers, especially those with pre-existing thyroid issues, are advised to have the health of their thyroid checked as soon as pregnancy is detected.

Any thyroid function abnormality can potentially influence the pregnancy outcomes for the mother and foetus at all stages of pregnancy. Therefore, women with active hyperthyroidism or hypothyroidism should be treated before attempting to get pregnant.^7,8

Poor control of thyroid hormone has been associated with complications such as:^7,8

• Miscarriages
• placental abnormalities
• pregnancy-induced hypertension
• premature delivery
• low birth weight
• stillbirth
• intellectual impairment in offspring

After delivery

New mothers who have not been previously diagnosed with thyroid disease can develop problems with their thyroid within the first year after giving birth; this is called postpartum thyroiditis (PPT).⁹
‍
The prevalence of PPT is approximately 5%. Women with underlying autoimmune disorders have an increased risk of PPT, with 44% in women with a prior history of Graves’ disease.⁹

PPT can have an initial phase of hyperthyroidism followed by hypothyroidism before resolving, but not all women appear to go through all the phases, with some only manifesting the hyperthyroid or hypothyroid phase in isolation.¹⁰

Almost half of the women with PPT may experience the symptoms of an under active thyroid. These include fatigue, loss of concentration, poor memory, constipation, and possible depression.⁹

About 30% of women who develop PPT may experience symptoms of an overactive thyroid. These include fatigue, palpitations, weight loss, heat intolerance, nervousness, anxiety and irritability.⁹

Treatment is not needed in all cases. Most women find their thyroid gland works normally by the end of the first year after the birth of their baby.⁹
Should you experience any of persistent symptoms of hyperthyroidism or hypothyroidism, please consult your doctor.

Summary

• A normal thyroid function is essential for ovulation, egg implantation and maintenance of a healthy pregnancy
• Women with active hyperthyroidism or hypothyroidism should be treated before attempting to get pregnant
• Most women with postpartum thyroiditis recover fully, but those with persistent symptoms of hyper or hypothyroidism should seek medical advice.