Treatment of autoimmune thyroid disease in pregnancy

Study 3- Negro et al (fig 2)

This was a study of pregnant women who were euthyroid in the early stages of pregnancy but who had positive thyroid autoantibodies (TPO-Abs). The goal was to see if any of these women would benefit from levothyroxine administration to reduce the rate of spontaneous miscarriage and premature delivery. Caucasian pregnant women (n = 984) was investigated between November 2002 and October 2004. Measurements of TPO-Abs and thyroid function tests were carried out at the first prenatal visit. Thyroid function tests were repeated at 20 and 30 weeks of gestation and finally 3 days after delivery. Among the cohort, 115 women (11.7%) had positive thyroid autoantibodies. The women with AITD were randomly assigned to two groups: group A (n = 57) received levothyroxine; group B (n = 58) received no treatment. women without AITD served as controls for thyroid function testing and pregnancy outcomes. Levothyroxine given as 0.5 µg/kg·d of levothyroxine (when serum TSH was < 1 µU/ml), 0.75 µg/kg·d (when TSH was 1–2 µU/ml), and 1 µg/kg·d (when TSH was > 2 µU/ml or presence of a high TPO-Ab titer: > 1500 kIU/liter). The trial design in this study was randomized and prospective but not placebo controlled or double blind.

The study confirmed previously know findings: 1) Euthyroid women with thyroid autoantibodies tend to be older when they become pregnant; 2) Even though euthyroid in early gestational stages, these women tend to have a reduced thyroid functional reserve 3) They have an increased risk for obstetrical complications (miscarriage and premature delivery) 4) When given the benefit of treatment with thyroid hormone, they normalize thyroid function tests and behave as control women.

New findings of the study: Levothyroxine administration to women with autoimmune thyroid disease (Hashimoto's) allowed for a significant decrease in the rate of obstetrical complications, with the miscarriage rate reduced by 75% (from 13.8 to ± 3.5%) and the frequency of premature delivery by 69% (from 22.4 to ± 7%); Note: There is no reason to believe that levothyroxine administration played a role in altering underlying autoimmunity. Also, the age difference between women with AITD and control women was not large enough to explain the different rates of miscarriage and premature birth and obviously even less the changes observed in such rates after treatment with levothyroxine

Should all pregnant women be screened for thyroid antibodies?:

There is no firm consensus on this topic. The endocrinologists at Houston Thyroid and Endocrine do check thyroid antibodies. If these antibodies are positive then the TSH goal in these women is 1.0 to 2.5 iU/L. This is the Endocrine Society August 2007 Guideline for autimmune thyroid disease and miscarriage: Although a positive association exists between the presence of thyroid antibodies and pregnancy loss, universal screening for antithyroid antibodies and possible treatment cannot be recommended at this time. As of this date, only one adequately designed intervention trial has demonstrated a decrease in the miscarriage rate in thyroid antibody-positive euthyroid women. USPSTF recommendation level is C; evidence is fair (grade 2 recommendation).