Background Approximately 15% of women of childbearing age have positive thyroid auto antibodies. Antibody positivity has been associated with adverse obstetric outcomes.

Aim To evaluate the evidence of association between positive thyroid autoantibodies in euthyroid women and obstetric outcomes.

To assess the effectiveness of levothyroxine (T4) treatment in euthyroid women antibody positive women in reducing spontaneous abortion and preterm labour.

Methods The authors searched MEDLINE, EMBASE, CCTR, CDSR, from database inceptions to 2009 without language restrictions.

Results The authors identified 29 studies, with 9817 women for the outcome of spontaneous abortion. Meta-analysis showed more than doubling in the odds of spontaneous abortion in the presence of antibody positivity (OR 2.41, 95% CI 1.91 to 3.05). Four studies, including a total of 2896 women, evaluated preterm birth as the outcome. Meta-analysis showed an increase in the odds of preterm birth in the presence of thyroid antibodies (OR 2.67, 95% CI 1.85 to 3.85).

Two randomised trials evaluated the effectiveness of T4 treatment on spontaneous abortion and preterm births in thyroid antibody positive euthyroid women. Meta-analysis showed a statistically significant 52% reduction in spontaneous abortions with T4 treatment (RR 0.48, 95% CI 0.25 to 0.92). One trial reported on preterm birth outcome, and found a 69% reduction in preterm births with T4 (RR 0.31, 95% CI 0.11 to 0.90).

Conclusion There is a strong association between positive thyroid autoantibodies and spontaneous abortion and preterm births. Treatment with T4 has the potential to reduce the rates of spontaneous abortion and preterm births in women with thyroid autoantibodies.