Subclinical Hypothyroidism Increased Risk for Miscarriage

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Miscarriage risk before 20 weeks of gestation is higher among women with untreated subclinical hypothyroidism.

New results suggest the risk for miscarriage before 20 weeks of pregnancy is higher among women with untreated subclinical hypothyroidism (SCH) than among euthyroid women.

Researchers of the systematic review and meta-analysis, which was published in PLoS One, aimed to determine the relationship between SCH and the risk for miscarriage before 20 weeks of pregnancy. They searched literature databases for relevant studies published between 1980 and 2015, selecting those that compared the miscarriage prevalence in pregnant women with SCH with that in women who were euthyroid.

A total of 9 cohort studies were chosen for the final analysis.

Results demonstrated a higher risk for miscarriage in women with untreated SCH compared with euthyroid pregnant women (relative risk [RR], 1.90; 95% CI, 1.59-2.27; P <.01). Furthermore, women with SCH in the international diagnostic criteria group were more likely to experience miscarriages than those in the American Thyroid Association (ATA) diagnostic criteria group (χ2 = 11.493; P <.01).

However, the rate of miscarriage did not significantly differ among women with treated SCH compared with euthyroid women (RR, 1.14; 95% CI, 0.82-1.58; P =.43).

In other data, the miscarriage risk for women with SCH with thyroid autoimmunity was increased compared with women with isolated SCH (RR, 2.47; 95% CI 1.77-3.45; P <.01), whereas women with isolated SCH had a higher risk for miscarriages than euthyroid women (RR, 1.45; 95% CI, 1.07-1.96; P =.02).

In addition, the researchers performed a heterogeneity test, forest plot, and Begg’s test that indicated no significant heterogeneity or publication bias among the included articles; a sensitivity analysis also revealed high stability for the study.

“SCH is a risk factor for miscarriage in women before 20 weeks of pregnancy, and early treatments can reduce the miscarriage rate,” the researchers concluded. “Regardless of the diagnostic criteria used, the miscarriage rate increased as long as a pregnant woman was confirmed to have SCH. The results show that the omission diagnostic rate may increase when the ATA diagnostic criteria are used.”

The researchers added that patients with SCH with thyroid autoimmunity have a higher prevalence of miscarriage, and patients with isolated SCH have a higher miscarriage rate than euthyroid women.

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Zhang Y, Wang H, Pan X, Teng W, Shan Z. Patients with subclinical hypothyroidism before 20 weeks of pregnancy have a higher risk of miscarriage: a systematic review and meta-analysis [published online April 17, 2017]. PLoS One. doi:10.1371/journal.pone.0175708