Maternal adiposity, smoking, and thyroid function in early pregnancy.

Area of Science:

• Endocrinology
• Reproductive Medicine
• Public Health

Background:

• Deiodinase type 2 activity is hypothesized to be elevated in overweight, obese, and smoking pregnant women.
• This elevation is suggested by an increased triiodothyronine (T3)/thyroxine (T4) ratio.
• The relationship between maternal adiposity, smoking, and thyroid function tests in early pregnancy requires further investigation.

Purpose of the Study:

• To investigate the association between maternal adiposity (overweight or obesity) and smoking with thyroid function tests in early pregnancy.
• To explore how these factors influence thyroid-stimulating hormone (TSH) and the T3/T4 ratio.

Main Methods:

• A cross-sectional study was conducted using data from the North Denmark Region Pregnancy Cohort.
• Maternal TSH, total T4 (TT4), total T3 (TT3), free T4 (fT4), and free T3 (fT3) were measured in blood samples from 5529 pregnant women at a median gestational week of 10.
• Multivariate linear regression analysis was used to assess associations, adjusting for maternal age, parity, origin, gestational week, and diabetes.

Main Results:

• Maternal adiposity was associated with higher TSH (aβ 1.13), while maternal smoking was associated with lower TSH (aβ 0.875).
• Both maternal adiposity and smoking were independently associated with a higher T3/T4 ratio (free T3/free T4 and total T3/total T4).
• Approximately 40% of women had adiposity, and 10% were smokers.

Conclusions:

• Maternal adiposity and smoking exhibit opposing associations with TSH levels in early pregnancy.
• Both adiposity and smoking are linked to an increased T3/T4 ratio in early pregnancy.
• This finding may suggest altered deiodinase activity in response to adiposity and smoking during pregnancy.