Variability in thyroid-stimulating hormone suppression by human chorionic [corrected] gonadotropin during early...

Area of Science:

• Endocrinology
• Reproductive Medicine
• Maternal-Fetal Medicine

Background:

• Thyroid hormone levels are critical during pregnancy for both maternal and fetal well-being.
• Human chorionic gonadotropin (hCG) is known to influence thyroid function during gestation.
• Understanding the interplay between hCG, TSH, and free T4 is essential for accurate thyroid assessment in pregnant women.

Purpose of the Study:

• To investigate the relationship between human chorionic gonadotropin (hCG), thyroid-stimulating hormone (TSH), and free thyroxine (free T4) in pregnant women between 11 and 18 weeks of gestation.
• To explore how maternal factors influence these hormonal levels.

Main Methods:

• Analysis of paired first- and second-trimester sera from 9562 women participating in the First and Second Trimester Evaluation of Risk for Fetal Aneuploidy trial.
• Correlational and multivariate analyses were performed to assess relationships between hCG, TSH, free T4, and maternal covariates like body mass index, smoking, and gravidity.

Main Results:

• hCG showed strong correlations with body mass index, smoking status, and gravidity.
• Weak correlations were observed between hCG and TSH (r² = 0.03-0.02) and between hCG and free T4 (r² = 0.06-0.003).
• TSH concentrations at lower centiles were disproportionately suppressed at higher hCG levels, while free T4 levels increased uniformly at all centiles between 11-13 weeks gestation as hCG increased.

Conclusions:

• Maternal TSH centile level appears to influence susceptibility to TSH suppression at a given hCG level in early pregnancy.
• hCG is likely the primary analyte responsible for stimulating the maternal thyroid gland.
• The effect of hCG on TSH suppression is disproportionately greater on lower centile TSH values.