The thyroid is a butterfly-shaped gland in the base of your neck just below the Adam’s apple. It produces several hormones, all of which play an important role in your body's metabolism-- and your fertility.
This post covers the top ten ways your thyroid can impact your ability to get and stay pregnant-- particularly hypothyroidism (the most common thyroid disorder).
1. T4 Hormone Levels are Key
The most important hormone created by the thyroid gland is thyroxine (T4), which controls the body’s metabolism.If there is too much (hyperthyroidism) or too little T4 (hypothyroidism), the body does not function normally.
2. Thyroid Disorders are Quite Common
According to The Thyroid Foundation of America, there are as many as 8 million women in America with untreated thyroid disorders (about 1% of women). For those of reproductive age, infertility or miscarriage may be the first sign that something is wrong.
3. Hypothyroidism Slows the Metabolism
3) What are the symptoms of hypothyroidism? The slowed-down metabolism associated with hypothyroidism can manifest as fatigue, dry skin, constipation, heavier periods, weight gain, decrease in appetite, lethargy, depression, cold intolerance, or muscle aches.
4) How Hypothyroidism Causes Infertility
Hypothyroidism can cause infertility by preventing ovulation—even when menstrual periods are occurring regularly.
Women with undiagnosed hypothyroidism who do conceive have an elevated risk of miscarriage. And even hypothyroid women who’ve already been diagnosed, treated, and stabilized with medication need to be monitored closely.
Some women with an underactive thyroid may experience elevated levels of prolactin, the hormone that induces the production of breast milk in postpartum women. Excess prolactin can make conceiving more difficult, again by preventing ovulation.
Hypothyroidism’s effects on metabolism can also bring on a condition known as luteal phase defect. The luteal phase is the second half of the monthly cycle, lasting from ovulation to menstruation. It is normally 12 to 16 days long. But if the luteal phase chronically runs shorter than ten days, then there will be fertility problems since the uterine lining can’t build up sufficiently for the embryo to implant, and it will be flushed from the body with the next menstrual period.
5) How Hypothyroidism is Diagnosed
A simple blood test to measure thyroid stimulating hormone (TSH) level is used to diagnose hypothyroidism. TSH works like a thermostat; it’s produced by the pituitary gland to regulate thyroid function. An elevated TSH level is used to diagnose hypothyroidism. It indicates that the pituitary gland is attempting to compensate for an underactive thyroid gland.
6) Hashimoto's Thyroiditis and Slow Thyroid Function
There’s also a blood test that checks for the presence of anti-thyroid antibodies. High levels of these antibodies are typical of a thyroid disease called Hashimoto’s Thyroiditis, which always results in hypothyroidism. Hashimoto’s Thyroiditis is classified as an autoimmune disease, because the body has essentially turned against itself, forming antibodies that attack the cells in the thyroid and slow down production of thyroid hormone. The gland itself may compensate by becoming enlarged.
Sub-clinical hypothyroidism means that there are no symptoms. The only way of diagnosing this condition is with a blood test (TSH level). With elevated TSH levels, the quality of eggs retrieved is compromised. This results in lower pregnancy rates. It is therefore important that the TSH level be normalized prior to an IVF cycle.
8) Treating Hypothyroidism is Simple
To regulate thyroid levels, we prescribe oral synthetic thyroid tablets (Synthroid, Levoxyl, Levothyroxine). The goal is to treat with the lowest effective dose to maintain the TSH level close to (or just below) 2.5. While establishing the correct dose can be quite easy in some individuals, others will fluctuate up and down before stabilizing.
9) You Need 30 – 50% More TSH During Pregnancy
TSH levels should be checked every 3 months during pregnancy and annually thereafter. During pregnancy, an endocrinologist or an obstetrician that’s familiar with thyroid issues should monitor blood levels closely. Uncorrected hypothyroidism can result in stillbirth. I will often tell patients that taking their thyroid pill is as important (if not more) as taking their vitamins!
10) Thyroid Disorders are Easy to Correct For
The good news is that among the various threats to fertility, thyroid disorders are arguably the easiest to identify and treat.
Dr. Karande is Board Certified in the specialty of Obstetrics and Gynecology as well as the subspecialty of Reproductive Endocrinology and Infertility. He is a Fellow of the American College of Obstetricians and Gynecologists and Member of the American Society for Reproductive Medicine.