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To successfully conceive requires an interplay between a variety of hormones. For an ovarian follicle, which contains the immature ovum or egg, to be released requires adequate levels of female sex hormones including estrogen and progesterone - as well as normal levels of thyroid hormone.This raises an important question - does hypothyroidism cause infertility?
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What is Hypothyroidism?
Hypothyroidism is a condition where the thyroid gland, located in the neck, doesn’t produce enough thyroid hormone, a hormone involved in regulating metabolism. Hypothyroidism can occur because the thyroid gland doesn’t produce enough hormone due to disease of the thyroid itself or because the pituitary gland in the brain doesn’t send the proper signals to the thyroid gland to produce adequate amounts.
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Does Hypothyroidism Cause Infertility?
Most experts believe that hypothyroidism makes it more difficult for a woman to conceive, although most studies don’t show that the incidence of infertility is greatly increased in women with very mild or sub-clinical hypothyroidism. Despite this, low levels of thyroid hormone frequently cause changes in a woman’s menstrual cycle, which suggests that the sex hormones involved in fertility and reproduction are affected by a lack of thyroid hormone. It can also affect ovulation and when ovulation doesn’t occur, conception can’t take place.
It isn’t surprising that hypothyroidism would affect fertility since the production of normal levels of thyroid hormone depends on interaction between the hypothalamus and pituitary gland in the brain and the thyroid gland in the neck. The pituitary gland and hypothalamus are also involved in stimulating the ovaries to produce sex hormones like estrogen that are needed for fertility and development of the fertilized egg.
Thyroid hormone also affects prolactin levels, the hormone that stimulates milk production by the breasts for breastfeeding. Too much prolactin may cause irregular menstrual periods, prevent ovulation and make it more difficult to conceive.
The exact way in which thyroid hormone affects fertility isn’t completely understood, but there’s little doubt that inadequate levels of thyroid hormone affect hormones that are important for conception including estrogen, progesterone and prolactin.
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Autoimmune Hypothyroidism Also Causes Infertility
A special type of hypothyroidism called autoimmune hypothyroidism where the body produces antibodies against the thyroid gland also presents problems for women who wish to conceive. One type of autoimmune hypothyroidism called Hashimoto’s disease is a frequent cause of unexplained infertility.
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Hypothyroidism and Infertility: Is There a Treatment?
It’s important for a woman with hypothyroidism who wishes to conceive to get adequate treatment for her thyroid condition. Once the low levels of thyroid hormone are restored it may improve the chances of conceiving, but this isn’t always the case. If infertility is still a problem, most doctors instruct a woman to track whether she’s ovulating by using an over-the-counter kit available at the drugstore to document when ovulation occurs. If ovulation isn’t occurring, conception can’t either.
In some cases despite treatment of hypothyroidism, a woman is still unable to conceive. In this case, she may need in-vitro fertilization. It’s important to keep in mind that women who have autoimmune thyroid disease such as Hashimoto’s are at a higher risk of miscarriage even if they do conceive.
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Does Hypothyroidism Cause Infertility: The Bottom Line?
There is an association between hypothyroidism and infertility although the exact mechanisms aren’t completely understood. Normalizing thyroid hormone levels may help with conception, but, in some cases, in-vitro fertilization may be the only option.
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Medscape.com. "Thyroid Disease and Female Reproduction".
J Obstet Gynecol India Vol. 56, No. 1 : January/February 2006 Pg 68-71.
Merck Manual. Eighteenth edition. 2006.