Thyroid autoimmunity in pregnancy and its influences on maternal and fetal outcome in Iran (a prospective study)

Thyroid dysfunction and autoimmunity are common problems in women of child-bearing age. It could be associated with pregnancy morbidities in the mother and fetus. Due to lack of sufficient data about the prevalence of thyroid autoimmunity in pregnant women in Iran, and controversies about its complications on pregnancy outcomes, this study was conducted.

This is a prospective study on 600 singleton pregnant women in 15-28 weeks of pregnancy; they were residents of Fars province. We evaluated the prevalence of preeclampsia, intra-uterine growth retardation (IUGR), preterm delivery and low Apgar score and their association with TSH, thyroid peroxidase (TPO), and thyroglobulin (Tg) antibodies.

Prevalence of anti-TPO and anti-Tg positivity is 12.8% and 8.5% among Iranian pregnant women. Mothers with either positive TPO or Tg antibody have a higher risk of preeclampsia (p = 0.019), preterm delivery (p < 0.001), IUGR (p < 0.001), and low first minute Apgar score (p < 0.001). This association was independent of thyroid dysfunction for preterm delivery (RR = 5, p < 0.001), and low Apgar score neonates (RR = 8.8, p < 0.001), but this association for preeclampsia was due to thyroid dysfunction (RR = 3.7, p = 0.003). About IUGR in either TPO or Tg positive mothers, this association results from the additive effect of thyroid dysfunction and thyroid autoimmunity (RR = 8.3, p < 0.001). Cesarean section delivery was significantly higher in abnormal TSH/positive anti-Tg mothers (p = 0.045).

Thyroid autoimmunity independent of thyroid dysfunction could have significant adverse outcomes in the mother and fetus. Further investigation should be done to reveal the significance of screening and treating the thyroid autoimmunity during pregnancy.