The Thyroid is probably one of the most important glands for overall health. The optimal functioning of multiple Organ Systems depends on a Healthy Thyroid. The tiny little gland that can usually be palpated in the neck has far reaching effects on the Digestive system, skin health, hair health, cardiovascular system, the neurological system, and, you guessed it, the Reproductive System.
The standard for testing usually involves checking Thyroid-Stimulating Hormone (TSH) levels in the blood. TSH is a chemical messenger made in the pituitary gland that signals the Thyroid to increase its production of Thyroid Hormone. When the thyroid function slows down and becomes a bit sluggish, the Pituitary will increase the TSH it sends to the Thyroid. Similarly, when the Thyroid becomes a bit too active or hyper the Pituitary tries to balance its function by decreasing the production of TSH.
Classification of Thyroid Disorders
Thyroid disorders are divided in to two main categories: Hyperthyroidism and Hypothyroidism.
Hyperthyroidism is when the function of the thyroid goes above normal, and it causes, among other hormonal disruptions, an increase in Reproductive Hormones and its carrier in the blood (Sex-hormone binding globulin - SHBG). The increase in SHBG actually makes a larger percentage of the reproductive hormones unavailable for the body to use as it holds on to it and prevents it from binding to hormone receptors in the body.
Hypothyroidism can lead to, among many other symptoms, a decrease in Ovulatory function and reproductive hormone production (i.e. estrogen), and can lead to infertility.
Subclinical Hypothyroidism is when the blood has more TSH than normal (suggesting that thyroid function has decreased) but the individual has not noticed or presented any of the symptoms that point towards a slow thyroid. But this does not mean that there are no negative effects! Subclinical hypothyroidism is related to increased miscarriage rates and infertility.
Evaluating Thyroid Function:
The first step is looking at the TSH value in the blood, if it is above 5.0 mU/mL it is considered hypothyroidism, and if it is below 0.5 mU/L it is considered Hyperthyroidism. Further testing can be done to evaluate for specific auto-immune disorders that may be affecting thyroid function, among other tests that also give a better understanding of thyroid function (i.e. T4, T3, reverse T3, Thyroid releasing hormone -TRH).
Optimal Thyroid Function to Fertility:
Because Subclinical Hypothyroidism can actually lead to pregnancy complications (hypertension during pregnancy, gestational diabetes, poor cognitive development of the fetus, and increase the chances of miscarriage, there are guidelines suggesting that bringing down the TSH below 2.5 mU/L before pregnancy to help prevent maternal hypothyroidism and its complication.