Preconception body mass index and maternal thyroid function: a longitudinal observational study.

Area of Science:

• Reproductive endocrinology
• Maternal-fetal medicine
• Thyroidology

Background:

• Preconception body mass index (p-BMI) is a key factor in pregnancy health.
• Maternal thyroid function plays a crucial role in both maternal and fetal well-being.
• Understanding the interplay between p-BMI, thyroid hormones, and pregnancy outcomes is vital for optimizing prenatal care.

Purpose of the Study:

• To investigate the longitudinal association between preconception body mass index (p-BMI) and maternal thyroid function throughout pregnancy.
• To explore the relationship between early-pregnancy thyroid parameters and adverse obstetric outcomes.

Main Methods:

• 1,107 pregnant women were categorized by p-BMI: normal weight (NW), overweight (OW), and obesity (OB).
• Thyroid function (Thyrotropin [TSH] and free thyroxine [FT4]) was assessed longitudinally across three trimesters.
• Generalized estimating equations analyzed thyroid hormone trajectories; logistic regression examined associations with adverse obstetric outcomes.

Main Results:

• Women with higher p-BMI (OW, OB) had lower early-pregnancy FT4 and higher TSH compared to NW women.
• Throughout gestation, FT4 levels decreased while TSH increased across all p-BMI groups.
• First-trimester low FT4 was significantly associated with increased risk of adverse obstetric outcomes (OR 2.04), with a weaker association for elevated TSH (OR 1.71).

Conclusions:

• Elevated preconception BMI is associated with a sustained suboptimal maternal thyroid hormone profile during pregnancy.
• Early-pregnancy low FT4 concentrations represent a significant indicator of obstetric risk.
• Routine thyroid assessment in early pregnancy for women with higher p-BMI may help identify at-risk individuals.