Thyroid Research Thyroid Research Archive Hypothyroidism

Thyroxine therapy increases the pregnancy rate in women with mild thyroid hypofunction

(July 2003)

The background of the study. Women with hypothyroidism may be infertile, but whether women with infertility have hypothyroidism and the effect of thyroxine (T4) therapy on their infertility are uncertain. In this study, thyroid function was assessed in infertile women, and the effect of T4 therapy on infertility was determined in the women found to have hypothyroidism.

How the study was done. Women with infertility were evaluated for thyroid dysfunction as part of a standard work-up for their infertility. Women with obvious hypothyroidism or bilateral tubal obstruction were excluded, as were those whose partners had very low sperm counts. Thyroid status was assessed by measurements of serum T4 and thyrotropin (TSH). The 131 women who had any thyroid dysfunction were treated with T4. All women were seen at three-month intervals, and more often if they were pregnant.

The results of the study. The mean age of the 217 women who were followed was 32 years; 131 were treated with T4. They had been infertile for approximately 2.5 years. During a mean follow-up period of 20 months, 82 of the women (38 percent) became pregnant. The pregnancy, spontaneous abortion, and delivery rates were similar in women with thyroid dysfunction who were treated with T4 and those with normal thyroid function. All the abortions occurred during the first trimester, and they were not related to the presence of autoimmune thyroiditis.

The pregnancy rate was higher in younger women and in those in whom serum TSH concentrations were <2.5 mU/L during follow-up. In contrast, duration of infertility, duration of follow-up, or presence of autoimmune thyroiditis were not related to pregnancy.

The conclusions of the study. Women with minor degrees of thyroid hypofunction who are treated with T4 have pregnancy, abortion, and delivery rates similar to women with normal thyroid function.

The original article. Raber W, Nowotny P, Vytiska-Binstorfer E, Vierhapper H. Thyroxine treatment modified in infertile women according to thyroxine-releasing hormone testing: 5 year follow-up of 283 women referred after exclusion of absolute causes of infertility. Hum Reprod 2003;18:707-14.