P01.06: The effect of antenatal corticosteroids on the fetal thymus

Abstract

Despite the proven benefits of antenatal corticosteroids (ACS) in pregnancies at risk for preterm delivery, there have been concerns raised regarding the potential long-term risk of ACS on thymus development and immune function. The objective of this study is to demonstrate the effect of ACS on the size of the fetal thymus gland in pregnancies at risk for preterm delivery compared to gestational age-matched controls. Women with a singleton pregnancy at risk for preterm delivery who received Betamethasone and an equal number of gestational-age matched controls not at risk for preterm delivery who did not receive Betamethasone were included in the study. Fetal thymus perimeter and diameter were measured by 2D ultrasound at baseline and then 2 weeks after corticosteroid administration or enrollment into the study and were repeated every 2 weeks. The primary outcome was a difference in the change in thymus size from baseline to 2 weeks later for each gestational-age matched pair. A secondary outcome measure was a difference in the longitudinal analysis of thymus size at weekly intervals over 6 weeks. From March 2010 to April 2014, 31 gestational-age matched pairs were eligible for inclusion in the final analysis of the study. There was no significant difference in change in thymus perimeter or diameter from baseline to 2 weeks later in exposed and unexposed women. A significant difference was noted in the trajectories of thymus perimeter and diameter from baseline to 6 weeks, with a lower rate of increase in thymus size in exposed women compared to unexposed women. Our study did not find a significant difference in the thymus size from baseline to 2 weeks post-exposure to ACS, but the longitudinal trajectory of thymus size showed a significantly smaller thymus size in women exposed to glucocorticoids over time compared to unexposed women. This study raises concerns about the long-term effect of ACS on thymus development and immune programming.