Persistency of Thyroid Dysfunction from Early to Late Pregnancy

Area of Science:

• Obstetrics and Gynecology
• Endocrinology
• Reproductive Medicine

Background:

• Subclinical thyroid disease affects 5-8% of pregnancies, increasing risks of miscarriage, preterm birth, and developmental issues.
• Persistent subclinical thyroid disease is assumed to pose greater risks than transient forms.
• The persistence rate of early pregnancy thyroid dysfunction into the third trimester is not well-established.

Purpose of the Study:

• To determine the percentage of women with subclinical thyroid disease in early pregnancy who have persistent disease in the third trimester.
• To identify predictors of thyroid disease persistence throughout pregnancy.

Main Methods:

• Analysis of data from 42,492 mothers with available early and late pregnancy thyroid function tests (TSH, fT4, T3) and TPOAbs.
• Exclusion of women treated for thyroid conditions before or during pregnancy.
• Statistical adjustment for confounders including maternal age, parity, anthropometrics, and β-hCG.

Main Results:

• Persistence rates: Subclinical hypothyroidism (24.8%), hypothyroxinemia (17.7%), overt hyperthyroidism (8.4%), subclinical hyperthyroidism (20.9%), low T3 (43.4%), elevated T3 (15.7%), TPOAb positivity (84.0%).
• Lower TSH (<5 mU/L) at diagnosis reduced subclinical hypothyroidism persistence risk by up to 50%.
• Thyroid peroxidase antibody (TPOAb) positivity predicted persistence of all evaluated thyroid disease entities.

Conclusions:

• Untreated thyroid disease from early pregnancy persists into the third trimester in 8.4-24.8% of cases.
• TPOAb positivity is the primary predictor of persistence, associated with lower persistence of hypothyroidism/hypothyroxinemia but higher persistence of hyperthyroidism.