Background: Combined cardiac output (CCO) and cerebral autoregulation impact on fetal growth may vary in different congenital heart defects. This study compared serial measures of fetal growth, CCO, middle cerebral artery and umbilical artery pulsatility indices (PIs) as indicators for vascular resistance in four groups: hypoplastic left heart (HLHS), non-HLHS single ventricle (SV), transposition of great arteries (TGA) and normal controls.

Methods and results: Fetal echocardiograms from 109 fetuses were reviewed: HLHS (n=30), non-HLHS SV (n=20), TGA (n=17) and controls (n=42). CCO was calculated using valvar area, velocity time integral and heart rate. PIs were calculated using systolic, diastolic and mean velocities. Anthropometric measures were recorded. Regression models were used to study CCO, PIs and fetal anthropometric trends over gestational age. Multivariate analysis was used to determine the association of CCO and PIs at 30 weeks with birth weight, length and head circumference z-scores.

CCO increased in all 4 groups through gestation but plateaued in HLHS and SV at the end of gestation. Middle cerebral artery PI values were lower in HLHS compared to non-HLHS SV through gestation suggesting a different cerebral blood distribution. At the end of gestation, fetal weight plateaued in HLHS and SV (similar to CCO curves) and head circumference plateaued in all groups but controls. CCO positively correlated with birth weight z-scores (p=0.003) and birth length z-scores (p=0.04). There was a trend toward a positive association between CCO and head circumference z-score (p=0.06). PIs did not correlate with any of the birth measurements.

Conclusions: CCO positively correlates with birth weight and may provide one mechanism to understand differences in fetal growth in congenital heart defects. Different brain autoregulation mechanisms are noticed between the groups. A brain sparing mechanism in HLHS is supported by lower cerebral vascular resistance.