• Jennifer A Tioseco, Hany Aly, Jonah Essers, Kantilal Patel, and Ayman A E El-Mohandes.
• Department of Neonatology, The Children's National Medical Center, Washington, DC, USA.
• Pediatr Crit Care Me. 2006 Jan 1; 7 (1): 40-4.

BackgroundNeonatal mortality and morbidity are sex biased in low birth weight infants. The "Y chromosome effect" has been suggested to be responsible for these maturational differences.ObjectiveTo examine the association of sex and neonatal outcomes.Design And MethodsA retrospective observational study. Data on all low birth weight infants who survived for >48 hrs were analyzed. Neonatal outcomes were compared between male and female infants. A regression model was used to detect the influence of sex on outcomes after controlling for confounders. Analysis was repeated after stratification of infants into three groups: group A (<1000 g), group B (1000-1499 g), and group C (1500-2499 g).ResultsA total of 833 infants were included in this study; 419 female infants and 414 male infants. Male infants had an increased rate of overall intraventricular hemorrhage (IVH) (12.2% vs. 7.2%, p = .02) and IVH grades 3-4 (4.8% vs. 2.3%, p = .04). In addition, male infants had higher bilirubin levels (10.19 +/- 3.1 mg/dL vs. 9.32 +/- 2.94 mg/dL, p = .001). In a regression model, male sex continued to have significant influence on IVH, IVH grades 3-4, death, and bilirubin. In group A, male infants had a significantly increased prevalence of death (regression coefficient, 1.82 +/- 0.65; p = .005) that could not be explained by the increased prevalence of IVH (p = .18) in regression analysis. In group B, male sex was significantly associated with a higher bilirubin level (regression coefficient, 0.94 + 0.3; p = .002). In bivariate analyses, IVH and IVH grades 3-4 were significantly higher in male compared with female infants (19.8% vs. 3.9%, p < .0001) and (8.5% vs. 0.97%, p = .02), respectively, but these differences lost significance in multiple-regression analysis. In group C, male sex positively influenced the prevalence of IVH (regression coefficient, 1.7 +/- 0.57; p = .003). Bilirubin measured higher in male infants (11.38 +/- 2.87 mg/dL vs. 10.19 +/- 3.22 mg/dL, p = .0004), but the difference lost significance in regression analysis (regression coefficient, 0.21 +/- 0.31; p = .5).ConclusionsBilirubin, IVH, and death were significantly higher in male infants. In subgroup analysis, significance was retained in group A (<1000 g). Whether a single biological factor is responsible for these differences or perhaps a multi-causal process involving a complex interaction of physiologic, environmental, and pathologic responses needs to be further addressed in future research.

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