hyroid hormones act systemically to control metabolism. Because function of the thyroid gland is under the control of the hypothalamo-pituitary axis, changes in thyroid function can impact greatly on reproductive function before, during and after conception.
Thyroid disease is the most common endocrine condition affecting women of reproductive age.
This video summarizes the effect of thyroid disorders on reproductive health and the current evidence on how thyroid function should be optimized to improve reproductive outcomes.
The thyroid gland controls rate of metabolic processes throughout the body via the production of two hormones triiodothyronine and thyroxine (T4).
These hormones also have key roles in growth and development, particularly brain development.
1 Thyroid hormone release is under the control of the hypothalamus and anterior pituitary (Figure 1).
Thyroid disease is classically divided into hyperthyroidism and hypothyroidism, and the causes of thyroid disease are numerous (Table 1).
There is also a subset of patients who are euthyroid and have positive thyroid autoantibodies. The role of these antibodies in reproductive health has received increasing attention over recent years.
Thyroid hormones are crucial for normal development of your baby’s brain and nervous system. During the first trimester—the first 3 months of pregnancy—your baby depends on your supply of thyroid hormone, which comes through the placenta NIH external link.
At around 12 weeks, your baby’s thyroid starts to work on its own, but it doesn’t make enough thyroid hormone until 18 to 20 weeks of pregnancy.
Two pregnancy-related hormones—human chorionic gonadotropin (hCG) and estrogen—cause higher measured thyroid hormone levels in your blood. The thyroid enlarges slightly in healthy women during pregnancy, but usually not enough for a health care professional to feel during a physical exam.
Treatment for hypothyroidism involves replacing the hormone that your own thyroid can no longer make. Your doctor will most likely prescribe levothyroxine NIH external link, a thyroid hormone medicine that is the same as T4, one of the hormones the thyroid normally makes. Levothyroxine is safe for your baby and especially important until your baby can make his or her own thyroid hormone.
Your thyroid makes a second type of hormone, T3. Early in pregnancy, T3 can’t enter your baby’s brain like T4 can. Instead, any T3 that your baby’s brain needs is made from T4. T3 is included in a lot of thyroid medicines made with animal thyroid, such as Armour Thyroid, but is not useful for your baby’s brain development.
These medicines contain too much T3 and not enough T4, and should not be used during pregnancy. Experts recommend only using levothyroxine (T4) while you’re pregnant.
