What It Is
A condition in which an underactive thyroid gland produces too few hormones, thus slowing down the body’s metabolism. It is the most common thyroid disorder. A common cause of hypothyroidism is Hashimoto’s disease, an autoimmune disorder in which antibodies attack cells in the thyroid, causing it to produce less thyroid hormone.
Who Gets It
The American Association of Clinical Endocrinologists estimates that as many as 27 million Americans may have overactive or underactive thyroid, more than half of them undiagnosed. Eight of 10 people with thyroid disease are women.
An underactive thyroid can cause constipation, heavier periods, weight gain, decrease in appetite, lethargy, depression, cognitive problems, fatigue, dry skin, intolerance to cold, and muscle aches. Sometimes symptoms are so subtle that the condition goes unrecognized for years. Infertility or miscarriage may be the first sign that something is wrong.
How It's Diagnosed/Detected
Thyroid disorders are easily detected by simple blood tests that measure levels of the hormone thyroxine and TSH (thyroid stimulating hormone). TSH, produced by the pituitary gland, works like a thermostat to regulate thyroid function. Levels may become too high or too low as the pituitary attempts to compensate for an underactive or overactive thyroid gland.
How It Affects Fertility (And Pregnancy)
An underactive thyroid can cause infertility by preventing ovulation, even when a woman has regular periods. Women with undiagnosed hypothyroidism who do conceive have an increased risk of miscarriage.
Some women with underactive thyroid have elevated levels of prolactin, the hormone that induces production of breast milk after delivery. Excess prolactin can prevent ovulation. Hypothyroidism also can shorten the luteal phase of the menstrual cycle, which normally lasts about 12 to 16 days. If the luteal phase is shorter than 10 days, the uterine lining cannot build up sufficiently for an embryo to implant.
Hypothyroidism is treated with a synthetic version of the hormone thyroxine. The body responds as it would to the real thing.
Of the various threats to fertility, thyroid disorders are among the easiest to identify and treat. If you have symptoms that you think might be cause by an under active thyroid, insist on testing, even if doctors have dismissed your complaints. If you already are being treated for hypothyroidism, you can still conceive and have a healthy pregnancy with a little extra planning and vigilance. Your doctor should monitor blood levels closely to ensure that thyroid hormone levels are in the normal range.
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