UCSF

Background: Neonates with congenital heart disease are more likely to be small for gestational age. Few studies have investigated the effect of birth weight Z-score on outcomes after congenital heart surgery. Methods: Patients from the Society of Thoracic Surgeons Congenital Heart Surgery Database (2010 to 2016) undergoing cardiac surgery at a corrected gestational age ≤ 44 weeks were included, and classified as severely (birth weight Z-score -4 to -2), moderately (Z-score between -2 and -1) and mildly growth restricted (Z-score -1.0 to -0.5) and compared to a reference (Z-score 0 to 0.5). Multivariable logistic regression clustering on center was used to evaluate the association of birth weight Z-score with operative mortality, postoperative complications and length of stay, adjusting for other patient characteristics. Interaction between Z-score for birth weight and gestational age was assessed. Results: In 25,244 patients, operative mortality was 8.6% and major complications occurred in 19.4%. Compared to the reference group with no growth restriction, the adjusted odds (AOR) of mortality was increased in infants with severe (AOR 2.4, CI 2.0-3.0), moderate (AOR 1.7, CI 1.4-2.0) and mild growth restriction (AOR 1.4, CI 1.2-1.6). The AOR for major postoperative complications was increased for infants with severe (AOR 1.4, CI 1.2-1.7) and moderate growth restriction (AOR 1.2, CI 1.1-1.4), but not in mildly growth restricted infants (AOR 1.0, CI 0.9-1.2). Length of stay was prolonged for all growth restricted cohorts (adjusted Hazard Ratio<1, p<0.05 for all). There was significant interaction between birth weight Z-score and gestational age (p=0.007) with the strongest association between birth weight Z-score and operative mortality in early-term (gestational age 37-38 weeks), followed by full-term (>38 weeks) and then preterm infants (<37 weeks). Conclusions: Even birth weight Z-scores that are slightly below average are independent risk factors for mortality and morbidity in neonates undergoing cardiac surgery. The strongest association between poor fetal growth and operative mortality exists in early-term neonates. These novel findings may account for some of the previously unexplained variation in cardiac surgical outcomes.