Antenatal screening for thyroid dysfunction: pre-term birth, low birth-weight, and growth restriction

Area of Science:

• Obstetrics and Gynecology
• Endocrinology
• Perinatal Medicine

Background:

• Maternal thyroid function during pregnancy is crucial for fetal development.
• Thyroid screening in early pregnancy aims to identify dysfunction that could impact outcomes.
• The relationship between thyroid screening results and adverse pregnancy outcomes requires further clarification.

Purpose of the Study:

• To evaluate the association between maternal thyroid screening results and the incidence of pre-term birth, low birth-weight, and small for gestational age (SGA) infants.
• To determine if subsequent treatment influences these pregnancy outcomes.

Main Methods:

• A nested case-control study involving 10,052 asymptomatic pregnant women screened in the first trimester.
• Thyroid screening included anti-thyroid peroxidase antibodies, thyroid stimulating hormone, and free thyroxine.
• Cases (512) had positive screening results; controls (1292) had negative results. Outcomes assessed were pre-term birth, low birth-weight, and SGA.

Main Results:

• Women with positive thyroid screening results showed a significantly higher prevalence of pre-term birth (RR 1.69) and low birth-weight (RR 1.72) compared to controls.
• Low birth-weight was also increased in term pregnancies, though not statistically significant.
• No significant differences in pre-term birth or low birth-weight rates were observed among positive cases based on the type of treatment received.

Conclusions:

• Positive maternal thyroid screening results are linked to an increased risk of pre-term birth, independent of thyroid dysfunction or treatment.
• The association with low birth-weight is likely a consequence of the increased rate of early delivery.
• Routine thyroid screening may help identify pregnancies at risk for adverse outcomes like pre-term birth.