Untreated or improperly treated hypothyroidism can affect fertility in a number of ways.
If you are trying to get pregnant and have been unsuccessful, there is one essential thing you must do before you embark on costly or invasive fertility tests, or spend thousands of dollars for assisted reproduction: make sure your thyroid is functioning properly.
Many women -- and many doctors as well -- do not realize that thyroid function is necessary for fertility, essential to the ability to become pregnant, and must be maintained in order to sustain a healthy pregnancy -- even in the earliest days after conception.
Infertility is defined as the inability to conceive after one year of unprotected intercourse (six months if the woman is over age 35) or the inability to carry a pregnancy to live birth. Typically, a woman in this situation is advised to have a complete infertility workup.
But, surprisingly, despite the fact that millions of women in the U.S. have undiagnosed hypothyroidism -- a low, under-functioning thyroid that can prevent their ability to get pregnant -- women with infertility aren't told that their first step should be a thorough thyroid evaluation. This testing may not even be included in basic fertility workups.
A comprehensive thyroid evaluation should be done as soon as possible for any woman who wants to get pregnant and:
* has a family history of thyroid problems
* has an irregular menstrual cycle
* has tried unsuccessfully to get pregnant for more than six months
* has had more than two miscarriages
How Does Hypothyroidism Affect Fertility?
Untreated or improperly treated hypothyroidism can affect fertility in a number of ways.
Anovulation/Anovulatory Cycles -- Even in an anovulatory cycle -- where you don't release an egg -- you can have a period. This doesn't mean you are ovulating -- you can still build up and shed the lining. But anovulation makes pregnancy impossible.
Luteal Phase Defect -- Some women with untreated or undertreated hypothyroidism have a short luteal phase -- the time from ovulation to menstruation. Because this is the time when a fertilized egg properly implants in the uterus if it's too short, the egg won't implant securely, and ends up leaving the body at the same time menstruation would occur. This actually is a very early miscarriage but is often mistaken as a regular menstrual period.
High Prolactin Levels -- Some women have very high levels of prolactin, the hormone that stimulates milk production. This "hyperprolactinemia" may be due to elevated levels of Thyroid Releasing Hormone (TRH) seen in hypothyroidism. Hyperprolactinemia can cause irregular ovulation or anovulation, interfere with a regular menstrual cycle, and even cause milk production in a woman who is not breastfeeding.
Hormonal Imbalances -- An entire cavalcade of hormonal problems that can interfere with fertility can also result from hypothyroidism, including decreased sex hormone-binding globulin (SHBG); estrogen dominance; and progesterone deficiency. Any of these imbalances can interfere with proper reproductive hormone balance.
How to Evaluate the Thyroid
Your thyroid evaluation should include a physical examination. Your doctor will look for obvious signs of an underactive thyroid, including goiter (an enlarged neck), loss of hair in the outer edge of the eyebrows, a slow Achilles reflex, puffiness in the eyes, changes in the texture of hair and skin and hair, and other clinical signs. Your personal and family history of thyroid and autoimmune disease, as well as your symptoms, should also be carefully reviewed.
The comprehensive thyroid evaluation should include the following bloodwork:
* TSH: Thyroid Stimulating Hormone
* Total T4
* Free T4, Free T3
Thyroid autoimmunity testing -- tests for various antibodies against the thyroid -- should also be done. These tests include:
* Thyroid Peroxidase (TPO) Antibodies
* Thyroglobulin/Antithyroglobulin Antibodies
* Thyroid-Stimulating Immunoglobulins (TSI)
While many doctors don't think to test for antibodies, savvy patients and practitioners are recognizing the importance of this testing in women who want to become pregnant. Even among women with normal thyroid function and no history of pregnancy loss, the presence of thyroid antibodies doubles the risk of first-trimester miscarriage, substantially increases the risk of recurrent miscarriages, and may reduce the overall chance of successfully becoming pregnant in the first place.
Optimum Thyroid Level for Fertility
What's the best thyroid blood test level in order to become pregnant and maintain a successful pregnancy for both mother and baby? That's a difficult question because different doctors have different answers. Some women may have been told that their TSH test level is "normal," and they shouldn't have any trouble getting pregnant, yet they suffer years of "unexplained" infertility.
Currently, the recommended guidelines for the general population's normal range of TSH levels are from 0.3 to 3.0, but many experts suggest that a woman trying to conceive be kept at even lower levels, in the 1.0 to 2.0 range, in order to meet the increased demand that pregnancy puts on the mother's thyroid production early in pregnancy.
Treatment Helps Fertility
A number of studies have shown fertility improvements in women given thyroid treatment. When hypothyroidism is treated with thyroid hormone replacement, and levels are optimized, many women may find that cycles become more regular, and shorter cycles lengthen (evidence that the luteal phase is normalizing). These are all signs that underlying reproductive hormone imbalances are resolving.
Thyroid treatment can also help lower antibody levels, and counteract to some degree the negative effect antibodies can have on fertility. In one study of women who had thyroid antibodies, borderline hypothyroidism according to TSH levels, and a history of recurrent and early miscarriages, thyroid hormone was given before and during pregnancy. This significantly reduced the miscarriage rate, and 81% of the women had live births.
One important note: In a woman with low thyroid who is being treated, pregnancy should be confirmed as early as possible. There is often a dramatic increase in the dosage requirements for thyroid hormone during early pregnancy. A fetus has no thyroid function of its own until the 13th week of gestation, and so the mother's thyroid is forced to carry the load during that first trimester. Some women require as much as a 50% increase in their thyroid dosage amount to meet these hormonal demands of early pregnancy. Good thyroid control before conception, and early and frequent testing and readjustment of dosage throughout the pregnancy, are therefore essential to keep both mother and baby healthy.
And optimal levels need to be maintained and monitored throughout the pregnancy. According to new research just published in early 2006, the following are the TSH normal ranges for pregnant women:
* First Trimester: 0.24 - 2.99
* Second Trimester: .46-2.95
* Third Trimester: .43 - 2.78
Thyroid treatment is not the magic cure for all infertility, but there are, without question, women who will find that once their undiagnosed thyroid problem is properly treated, their fertility problems will be resolved, and they can go on to have a healthy pregnancy and the joys of motherhood.
