Infertility and Thyroid Disease

Couple looking at pregnancy test
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Infertility is defined as the failure to become pregnant after 12 months or more of unprotected intercourse. It's estimated that from 10 to 15 percent of couples in the United States experience infertility.

Some of the people who struggle with infertility go on to pursue assisted reproduction techniques, such as ovarian stimulation, in vitro fertilization, and other approaches. It's estimated that as many as 1% of all births in the United States are the result of assisted reproduction (fertility treatments), which on average, are successful in about 1 in 5 cases.

Many women don't realize that optimal thyroid function is essential to not only become pregnant—naturally and with the help of assisted reproduction—but to also maintain hormonal balance and protect the pregnancy during the crucial early days and first trimester.

If you are experiencing infertility or contemplating assisted reproduction, one crucial area of exploration should be your thyroid health. Surprisingly, some physicians, fertility clinics and fertility experts do not include a thyroid evaluation as part of a standard fertility workup, but women should insist on a comprehensive thyroid evaluation as soon as fertility challenges are suspected.

Here are some important tips to help you get started, adapted from the book Your Healthy Pregnancy with Thyroid Disease, published by Perseus Books and written by Dana Trentini and Mary Shomon.

The Thyroid's Effect on Fertility

Undiagnosed, untreated, or improperly treated thyroid disease increases your risk of a number of important factors that can affect your fertility, including the following:

  • an irregular menstrual cycle, which can make your fertile period erratic and difficult to pinpoint
  • menstrual cycles where you don't ovulate (release an egg) at all, and therefore can't conceive
  • a luteal phase (the period of time between ovulation and menstruation) that is too short to allow for successful implantation of an embryo. If fertilization is successful but the luteal phase is too short, the fertilized egg may be expelled during menstruation before a woman even realizes she's pregnant.
  • imbalances in estrogen and progesterone, which are essential for healthy fertility
  • autoimmunity that not only targets your thyroid, but can also target your ovaries, your partner's sperm, and other essentials for conception
  • less effective ovarian stimulation, in vitro fertilization and other assisted reproduction procedures

For optimal fertility, conventional medicine guidelines say that overt hypothyroidism— defined as a TSH level above 10 mIU/L—should be treated with thyroid hormone replacement drugs. If a woman is hypothyroid prior to pregnancy or diagnosed in early pregnancy, guidelines recommend that the dosage be adjusted so that TSH is below 2.5 mIU/L through the first trimester. During the second trimester, the TSH level should be maintained at a level of between 0.2 to 3.0 mIU/L, and 0.3 to 3.0 mIU/L in the third trimester. Levels outside these ranges can increase the risk of miscarriage, stillbirth, prematurity, and cognitive and other issues after a child is born.

Integrative physicians believe in being more aggressive for fertility, and treating women who have Hashimoto's disease (but otherwise "normal" thyroid levels), and when treating with thyroid hormone replacement, ensuring that not only is TSH below 2.5, but that Free T4 and Free T3 levels are in the upper half of the reference range.

Conventional guidelines state that any woman being treated for hypothyroidism will very likely require a thyroid hormone replacement dosage increase in very early pregnancy. The guidelines recommend confirming pregnancy early and increasing the dosage by an amount predetermined with the physician in advance.

If you are experiencing infertility:

  1. Get your TS) tested
  2. Get free T4 and free T3 tested
  3. Have thyroid peroxidase antibodies (TPO) tested
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