An article published in The Journal of Clinical Endocrinology and Metabolism in 2010 demonstrates an increased pregnancy loss rate in thyroid antibody negative women with a TSH level between 2.5 and 5 in the first trimester of pregnancy. The thyroid gland is an important endocrine organ involved in metabolism. Disruption of the thyroid can result in impaired reproductive function, including miscarriage.
Following are well known facts of pregnancy and thyroid function during pregnancy:
- On average 20% of all normal pregnancies end in miscarriage
- During pregnancy there is a 30-40% increased need for thyroid hormones due to increased placental uptake, increased thyroid binding globulin and increased blood volume
- Pregnant women with abnormal thyroid function experience increased rates of miscarriage, preterm deliveries, hypertension, diabetic complications, placental abruption, adverse fetal effects
- Women with anti-thyroid antibodies are 2 times more likely to experience a miscarriage
In this particular study, the authors (R. Negro, et al) studied 4123 women measuring their TSH levels during the first trimester. Findings:
- Of the 3481 women with a TSH level of < 2.5 mIU/L the miscarriage rate was 3.6%
- Of the 642 women with a TSH level of 2.5 – 5.0 mIU/L the miscarriage rate was 6.1%
- If anti-thyroid antibodies are present, giving levothyroxine during pregnancy decreased the spontaneous miscarriage rate from 13.8 to 3.5%
Because of these findings, the authors assert that, perhaps 2.5 should be the maximum normal value of TSH during pregnancy.
References: J Clin Endocrinol Metab 2010;95:E44-48
