Subclinical Hypothyroidism Increases Early Miscarriage Risk

Lara C. Pullen, PhD

November 25, 2014

A new study from China confirms that women who have subclinical hypothyroidism (SCH) as well as thyroid autoimmunity (TAI) are at increased risk for miscarriage between gestation weeks 4 and 8. In addition, women with the dual diagnosis had an earlier gestational age of miscarriage when compared with the general population.

The results support current recommendations from the American Thyroid Association. "Endocrinologists are more aggressive in offering levothyroxine to women with history of miscarriages and proof of [TAI] or with SCH," explained Christian Nasr, MD, medical director of the Thyroid Center at Cleveland Clinic in Ohio, to Medscape Medical News. "The [American Thyroid Association] also suggests trimester-specific thyroid-stimulating hormone goals when treating pregnant women," continued Dr Nasr, who was not affiliated with the study.

Haixia Liu, MD, from The First Hospital of China Medical University in Shenyang, and colleagues published the results of their prospective cohort study in the November issue of Thyroid. The study was designed to evaluate the association between subclinical thyroid abnormalities and risk for miscarriage during the first weeks of pregnancy.

The investigators included 3315 healthy women from iodine-sufficient regions. They excluded women who had high risk factors for thyroid disorders.

An isolated TAI with normal thyroid-stimulating hormone levels increased the risk for miscarriage (5.7% vs 2.2%; adjusted odds ratio, 2.71; 95% confidence interval [CI], 1.43 - 5.12; P = .003), whereas a combination of TAI and SCH increased the risk for miscarriage even more (10.0% vs 2.2%; adjusted odds ratio, 4.96; 95% CI, 2.76 - 8.90; P < .001).

Among those women who had a miscarriage, the miscarriage occurred at 6.5 ± 0.9 weeks in women with SCH and at 8.2 ± 2.1 weeks in healthy women with isolated positive thyroid peroxidase antibody.

"The results are not surprising. This is a larger cohort where women were screened and followed prospectively. Such study might be unethical in the USA with the present state of knowledge, because we already treat women with SCH or elevated autoantibodies with levothyroxine," explained Dr Nasr.

The results are also consistent with previous studies that have found an increased rate of pregnancy loss in women who are TAI-positive but have thyroid-stimulating hormone levels lower than 2.4 mIU/L. The authors note that at gestational weeks 4 to 8, thyroid autoantibody titers tend to be higher than at other weeks during pregnancy, as the normal immune suppression of pregnancy tends to be weakest at this time. Previous studies have shown that pregnant women with elevated thyroid antibodies during this time have improved pregnancy outcomes when given levothyroxine.

The women in the current study were not prescribed levothyroxine.

The authors and Dr Nasr have disclosed no relevant financial relationships.

Thyroid. 2014;24:1642-1649. Full text

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