According to new research conducted in Canada, the current practice of testing most pregnant women for thyroid-stimulating hormone (TSH) may be leading to overdiagnosis and overtreatment.

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The research was published in the CMAJ (Canadian Medical Association Journal). The study of more than 188 000 women in Alberta found that TSH testing was performed in more than half (111 522 or 59 percent) of all pregnant women who did not have thyroid disease before pregnancy. Testing was most commonly done around gestational week 5-6. "The practice of TSH testing early in the first trimester may be resulting in overdiagnosis and unnecessary thyroid hormone therapy during and after pregnancy," writes Dr. Lois Donovan, an endocrinologist at the Cumming School of Medicine, University of Calgary, with coauthors.

The challenge with TSH screening in pregnancy is that it identifies many women with very minor elevations in TSH, which is known as subclinical hypothyroidism. The best evidence shows no benefit for the mother or child from the treatment of pregnant women with subclinical hypothyroidism.

In 5050 (4.5 percent) pregnancies with TSH testing, women were started on thyroid hormone therapy; most (99 percent) received levothyroxine. Almost half of them (44.6 percent) continued with the treatment after giving birth, and almost one-third (31.5 percent) received 2 or more prescriptions in the first postpartum year. "This raises concerns about overmedicalization during pregnancy, given that minor, untreated TSH elevation usually normalized, as indicated by repeat measurement. The frequent postpartum continuation of thyroid hormone therapy for those who started it during pregnancy adds to this concern," write the authors.

Evidence-based clinical practice guidelines are needed to provide clinicians with the appropriate approach to decide whether and when TSH testing is required in pregnancy and when it is necessary to continue treatment in the postpartum period.