Thyroid-Stimulating Hormone (TSH)

Last Updated: April 10, 2019

Definition - What does Thyroid-Stimulating Hormone (TSH) mean?

Thyroid stimulating hormone (TSH) is responsible for controlling the function of the thyroid, which regulates metabolism and other biological functions. In women, TSH levels are critical to fertility and fetal development. Conception, development, and carrying a healthy pregnancy to term may be complicated or put at risk as a result of TSH abnormalities.

FertilitySmarts explains Thyroid-Stimulating Hormone (TSH)

The presence of excessive TSH is called hyperthyroidism. When this occurs, the body’s natural processes speed up. Too little TSH is called hypothyroidism, and the body’s processes slow down. Both conditions can be dangerous, and someone who experiences abnormal levels of TSH may be diagnosed with thyroid disease.

In order to test TSH, a blood test is required. The test results will provide a nominal value for the amount of TSH present in the blood. Scores from .4 to 4 mIU/L are considered normal.

However, scores for pregnant women may look different, as higher levels of TSH are needed. Low levels of TSH during pregnancy can be harmful to the developing fetus. Up until 12 weeks gestation, the fetus is dependent upon the mother’s thyroid for brain and nervous system development. This is particularly critical for women with hypothyroidism, as the fetus would not receive the appropriate amounts of TSH needed to foster healthy development.

An underactive thyroid (hypothyroidism) may cause:

  • Frequent menstrual periods (polymenorrhea)
  • Weight gain
  • Tiredness
  • Feeling cold

An overactive thyroid (hyperthyroidism) may cause:

  • Irregular menstrual periods (oligomenorrhea)
  • Anxiety and nervousness
  • Weight loss
  • Rapid heart weight
  • Heat intolerance, or hot flashes

During pregnancy, the following conditions are associated with the presence of thyroid disease:

  • Preeclampsia
  • Miscarriage
  • Low birth weight

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