Lactation Duration and Long-Term Thyroid Function: A Study among Women with Gestational Diabetes

Area of Science:

• Endocrinology
• Reproductive Health
• Metabolic Disorders

Background:

• Lactation is linked to reduced postpartum weight and lower cardiometabolic risk.
• Gestational diabetes mellitus (GDM) increases risk for future metabolic complications.
• Long-term thyroid function post-GDM requires further investigation.

Purpose of the Study:

• To examine the association between lactation duration and long-term thyroid function.
• To assess thyroid stimulating hormone (TSH), free triiodothyronine (fT3), and free thyroxine (fT4) levels in women with a history of GDM.
• To explore if lactation influences thyroid hormone levels years after pregnancy.

Main Methods:

• Study included 550 women with GDM history from the Danish National Birth Cohort.
• Follow-up data collected in the Diabetes & Women's Health Study (2012–2014).
• Adjusted associations between cumulative lactation duration and thyroid hormone concentrations (TSH, fT3, fT4) were assessed.

Main Results:

• Longer cumulative lactation duration correlated with higher fT3 levels (p-trend = 0.05).
• In women with a single pregnancy (n=70), >6 months of lactation was associated with higher fT3 (p-trend = 0.02) and fT3:fT4 ratio (p-trend = 0.007).
• These associations were observed 9–16 years postpartum.

Conclusions:

• Extended lactation duration may be associated with favorable long-term thyroid hormone profiles (higher fT3, fT3:fT4 ratio) in women with GDM history.
• The findings suggest a potential protective effect of lactation on thyroid function in this high-risk group.
• The association was particularly evident in women with a single lifetime pregnancy, suggesting parity as a potential modifier.