Thyroid function in pregnancy and its influences on maternal and fetal outcomes

Maternal thyroid function alters during pregnancy. Inadequate adaptation to these changes results in thyroid dysfunction and pregnancy complications.

This prospective study aimed to evaluate the prevalence of thyroid diseases in pregnancy and its outcomes in south of Iran.

This prospective study was conducted on 600 healthy singleton pregnant women who aged 18 to 35 years old at 15 to 28 weeks of gestation. We investigated the prevalence of thyroid dysfunctions in women. Multivariate analysis was performed to determine the effect thyroid dysfunction on obstetric and neonatal outcome.

Thyroid stimulating hormone (TSH) levels of 0.51, 1.18, 1.68, 2.4, and 4.9 mIU/L were at 2.5th, 25th, 50th, 75th, and 97.5th percentile in our population. The prevalence of clinical hypothyroidism, subclinical hypothyroidism, overt hyperthyroidism, and subclinical hyperthyroidism in all pregnant women was 2.4%, 11.3%, 1.2%, and 0.3%, respectively. In addition, 1.4% of patients had isolated hypothyroxinemia. Clinical hypothyroidism was associated with increased risk of preterm delivery (P = 0.045). Subclinical hypothyroidism had a significant association with intrauterine growth restriction (IUGR) (P = 0.028) as well as low Apgar score at first minute (P = 0.022). Maternal hyperthyroidism was associated with IUGR (P = 0.048).

We revealed that thyroid dysfunction during pregnancy was associated with IUGR and low Apgar score even in subclinical forms. Further studies are required to determine whether early diagnosis and treatment of thyroid diseases, even in subclinical form, can prevent their adverse effect on fetus.