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High serum antithyroid antibody values are a risk factor for miscarriage

(March 2005)

The background of the study. Spontaneous miscarriage is common. High serum antithyroid antibody concentrations, a marker for autoimmune thyroid disease, may be a risk factor for miscarriage. In this study, serum antithyroid antibodies and thyroid function were measured in a large group of pregnant women, and they were followed to determine the frequency of spontaneous miscarriage.

How the study was done. The study subjects were 534 women (mean age, 24 years) attending a prenatal clinic in Rio de Janeiro who were 5 to 12 weeks pregnant. Serum antithyroid peroxidase (TPO) antibodies, thyrotropin (TSH), and free thyroxine (T4) were measured at the first visit, and the women were followed thereafter. Miscarriage was defined as the spontaneous ending of pregnancy before 20 weeks.

The results of the study. Among the 534 women, 29 (5 percent) had a high serum anti-TPO antibody concentration. Their serum TSH concentrations, but not serum free T4 concentrations, were higher than the concentrations in the women with normal serum antibody concentrations.

Thirteen women (2 percent) had a spontaneous miscarriage. The rate was higher in older women and women with high serum anti-TPO antibody or high serum TSH concentrations (Table).

Table. Risk of Miscarriage as a Function of Age and Serum Anti-TPO Antibody and TSH Concentrations.
Miscarriage (%)
Age (yr)
10 (2%)
3 (8%)
High serum anti-TPO antibody
10 (2%)
3 (10%)
Serum TSH (mU/L)
1 (2%)
10 (2%)
2 (12%)

The conclusions of the study. The risk of spontaneous miscarriage is increased in older women and in women with high serum anti-TPO antibody and high serum TSH concentrations.

The original article. Sieiro Netto L, Medina Coeli C, Micmacher E, Mamede Da Costa S, Nazar L, Galvao D, Buescu A, Vaisman M. Influence of thyroid autoimmunity and maternal age on the risk of miscarriage. Am J Reprod Immunol 2004;52:312-6.

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