Background: Low birth-weight (bw) and unfavourable intrauterine conditions are associated with a subsequent impact on the endocrine system. However, very little is known about the impact on thyroid function.
Objective and hypotheses: We observed genetically identical twins with intra-twin bw-differences from birth until adolescence to objectify the impact of a lower bw on development and health in later life.
Method: Bw-difference of <1SDS was defined concordant, bw-difference >1SDS discordant. Blood sampling was performed at a mean age of 10.1 years (n=27 twinpairs; 15 discordant), 15.1 years (n=35 twinpairs, 15 discordant) and 17.4 years (n=36 twinpairs; 15 discordant). 18 twinpairs were seen at all three time-points.
Results: Group comparison revealed the following results: No significant differences in TSH, T3, and T4 levels were observed in the concordant twins. In the discordant group, a significant difference between the two twins for TSH levels was found at 10.1 years (P=0.041) and a tendency at 15.1 years (P=0.083). The smaller twins had higher mean TSH concentrations than their larger co-twins (10.1 years: 3.6 vs 2.5 μU/ml, 15.1 years: 2.6 vs 2.2 μU/ml). Again in the discordant group, significant differences in T4-levels were observed at 10.1 years (P=0.05) and 17.4 years (P=0.03) and a tendency at 15.1 years (P=0.08). The smaller twins showed lower T4 mean concentrations than their larger co-twins at all time-points (10.1 years: 7.8 vs 8.2 μg/dl, 15.1 years: 6.9 vs 7.4 μg/dl, 17.4 years: 7.7 vs 8.4 μg/dl). Calculation of the TSH-T4-ratio revealed significant differences in the discordant group, with a constantly higher ratio in the smaller twin: at 10.1 years (0.5 vs 0.3; P=0.006) and at 15.1 years (0.4 vs 0.3; P=0.04). Thyroid-antibodies were analysed and showed no significant differences. By calculating the BMI-SDS we found that in all twin-pairs and at all time-points, the smaller twins had a significant lower BMI-SDS than their larger co-twins (10.1 years: −0.70 vs −0.17 SDS; P=0.002, 15.1 years: −0.55 vs −0.15 SDS; P<0.001, 17.4 years: −0.26 vs 0.14 SDS; P<0.001).
Conclusion: In this special group of monozygotic twins with intra-twin bw-differences, we could show that birth-weight has a long-lasting impact on thyroid function. The significantly higher TSH concentrations, significantly lower T4 concentrations and elevated TSH-T4-ratios in the smaller twins who were born with a greater bw-difference indicate the possibility of a TSH-resistance and persisting low-T4 in low-birthweight children.
27 - 29 Sep 2018
European Society for Paediatric Endocrinology