Association between Z-score for birth weight and postoperative outcomes in neonates and infants with congenital heart disease

Objective: We hypothesized that infants with fetal growth restrictions have increased mortality and morbidity after congenital heart disease surgery.

Methods: The study included patients in The Society of Thoracic Surgeons Congenital Heart Surgery Database (2010-2016) who underwent cardiac surgery at a corrected gestational age of ≤44 weeks. Patients were classified as severely (birth weight Z-score -4 to -2), moderately (Z-score -2 to -1), and mildly growth restricted (Z-score -1.0 to -0.5) and compared with a reference population (Z-score 0-0.5). Multivariable logistic regression clustering on center was used to evaluate the association of birth weight Z-score with operative mortality and postoperative complications and its interaction with gestational age was assessed.

Results: In 25,244 patients, operative mortality was 8.6% and major complications occurred in 19.4%. Compared with the reference group, the adjusted odds ratio (AOR) of mortality was increased in infants with severe (AOR, 2.4; 95% confidence interval [CI], 2.0-3.0), moderate (AOR, 1.7; 95% CI, 1.4-2.0), and mild growth restriction (AOR, 1.4; 95% CI, 1.2-1.6). The AOR for major postoperative complications was increased for severe (AOR, 1.4; 95% CI, 1.2-1.7) and moderate growth restriction (AOR, 1.2; 95% CI, 1.1-1.4). There was significant interaction between birth weight Z-score and gestational age (P = .007).

Conclusions: Even birth weight Z-scores slightly below average are independent risk factors for mortality and morbidity in infants who undergo cardiac surgery. The strongest association between poor fetal growth and operative mortality exists in early-term infants. These novel findings might account for some of the previously unexplained variation in cardiac surgical outcomes.