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Subclinical hypothyroidism, ovarian hyperstimulation linked to intermediate rise in TSH
Thyroxine use resulted in a lower TSH, but did not have an influence on the level of thyroid autoantibodies.
In pregnant woman, subclinical hypothyroidism and ovarian hyperstimulation were associated with an intermediate risk in serum thyrotropin. However, the pattern of thyroid function during early pregnancy was unlikely to be associated with the higher miscarriage rate in women with subclinical hypothyroidism.
Researchers conducted a prospective, cohort study to examine thyroid function in early pregnancy in women with subclinical hypothyroidism who received levothyroxine replacement.
They enrolled eight women with subclinical hypothyroidism and eight euthyroid women. Thyroid function was assessed before pregnancy and serum sampling was collected on a weekly basis from week five to week 12 during pregnancy. Women with subclinical hypothyroidism were assigned to a fixed daily dose of 50 mcg thyroxine until week 12. The primary outcomes included weekly changes in T4, thyrotropin, thyroglobulin, triiodothyronine, human chorionic gonadotropin, estradiol, progesterone and prolactin.
At baseline, women with subclinical hypothyroidism had significantly higher thyroid-stimulating hormone levels compared with euthyroid women.
During the observation period, women with subclinical hypothyroidism who received T4 supplementation had higher TSH levels. Both groups experienced a peak in TSH levels at week six of pregnancy, including two women with subclinical hypothyroidism who had TSH levels ≥4.5 IU/L during week six and seven. The peak in TSH levels paralleled rising estrogen levels, according to the researchers. TSH levels declined between weeks nine and 12.
“Although the pregestational levels of TSH were significantly higher among women with subclinical hypothyroidism as compared with euthyroid controls, the self-limited estrogen-induced increment of TSH during early pregnancy was similar in both groups,” the researchers wrote.
Two women — one in each group — had a miscarriage during week 10 of pregnancy. The other 14 women had uncomplicated pregnancies and delivered healthy children. – by Katie Kalvaitis
Thyroid. 2009;19:53-59.
In this small, prospective study of women undergoing fertility treatment, those with subclinical hypothyroidism were given a fixed dose of 50 mcg T4, sufficient to normalize serum TSH before pregnancy. The finding that thyroid function tests generally did not differ in the first 12 weeks of pregnancy between euthyroid and T4-treated subclinical hypothyroid patients is not especially surprising. As suggested by the authors, these patients were mostly thyroid autoantibody negative (six of eight patients), and may have had significant residual thyroid that responded to the elevated human chorionic gonadotropin. Even with T4 treatment, however, serum TSH was higher in the subclinical hypothyroid patients at weeks 6 and 8. Although the authors may be correct that thyroid autoantibodies are the major factor in the higher rate of miscarriages in these patients, these data do not directly address this issue. A larger, prospective, randomized study has recently shown a reduced rate of miscarriage with T4 treatment for women with positive antibodies and TSH levels in the upper-normal range. The T4 treatment resulted in a lower TSH, but did not have an influence on the level of thyroid autoantibodies. The relative importance of maternal thyroid hormone levels and thyroid autoantibodies in the pregnancy-related complications of pregnancy, especially in the first trimester, remain an important area of study.
– Gregory A. Brent, MD
Endocrine Today Editorial Board member