Early structural cardiovascular changes on neonatal echocardiography after adverse intrauterine circumstances in identical twins.

Background: Studies on cardiovascular changes after fetal growth restriction (FGR) are limited by their design in which growth-restricted neonates are compared to appropriately-grown neonates. We aim to investigate early structural cardiovascular remodeling after FGR in identical twins, controlling for confounding of genetic and maternal factors.

Methods: This study is part of a prospective cohort study including monochorionic twins from January 2019. Transthoracic echocardiography was performed within one week after birth. Z-scores for cardiac valve annuli diameters and left ventricle dimensions based on gestational age at birth were compared between smaller and larger twins. Z-score differences between birth weight and cardiac structure per twin were tested against the intercept.

Results: Median gestational age at birth of the 100 included twin pairs was 33.8 (interquartile range (IQR) 30.8-36.1) weeks, with birth weights of 1729 (IQR 1200-2115) grams for smaller twins and 2058 (IQR 1643-2500) grams for larger twins. Smaller twins had a lower z-score for all structures. Z-score differences in birth weight and cardiac structure were higher than the intercept.

Conclusion: While cardiac structures are generally smaller for the twin with the lower birth weight, the deviation in birth weight tends to be more pronounced than the deviation in cardiac structure.

Impact: Our study shows that in identical twins, the smaller twin at birth has a structurally smaller heart on neonatal echocardiography when compared to the larger twin. Yet, cardiac structures per individual twin are less affected than body size for their given gestational age at birth. We have used a unique natural experiment by studying a population of identical twins with varying degrees of birth weight discordance, eliminating any confounding of genetic, maternal and obstetrical factors. Our results are suggestive of early cardiovascular remodeling after adverse intrauterine circumstances. This provides insight into the fetal programming of cardiovascular disease.