Thyroid Function in Monozygotic Twins with Intra-twin Birth Weight Differences: A Prospective Longitudinal Cohort...

Area of Science:

• Endocrinology
• Pediatrics
• Genetics

Background:

• Birth weight (BW) is a critical indicator of fetal growth and can influence long-term health.
• Thyroid hormones play a vital role in growth and development from infancy through adolescence.
• Understanding the impact of BW on thyroid function is crucial for identifying potential developmental issues.

Purpose of the Study:

• To investigate the long-term effects of intra-twin birth weight differences on thyroid function.
• To analyze thyroid function from childhood to adolescence in monozygotic twins with varying BWs.

Main Methods:

• Studied 52 monozygotic twin pairs with intra-twin BW differences.
• Assessed thyroid function (TSH, thyroxine) at mean ages of 10.1, 15.1, and 17.4 years.
• Defined BW difference of <1 SDS as concordant and ≥1 SDS as discordant.

Main Results:

• In discordant twins, smaller individuals had higher TSH and lower thyroxine levels compared to larger co-twins.
• Significant differences in TSH and thyroxine were observed at 10.1 and 17.4 years.
• TSH-thyroxine ratios were significantly higher in smaller twins at 10.1 and 15.1 years.

Conclusions:

• Birth weight differences in monozygotic twins appear to have a lasting impact on thyroid function.
• Low birth weight may be associated with delayed hypothalamic-pituitary-thyroid axis maturation.
• This suggests potential TSH resistance in children with lower birth weights during childhood and adolescence.