Sex-Specific Long-Term Trends in Length of Hospital Stay, Postmenstrual Age at Discharge, and Survival in Very Low Birth Weight Infants

Abstract

Introduction: In very low birth weight (<1,500 g, VLBW) infants, morbidity and mortality have decreased substantially during the past decades, and both are known to be lower in girls than in boys. In this study, we assessed sex-specific changes over time in length of hospital stay (LOHS) and postmenstrual age at discharge (PAD), in addition to survival in VLBW infants. Methods: This is a single-center retrospective cohort analysis based on quality assurance data of VLBW infants born from 1978 to 2018. Estimation of sex-specific LOHS over time was based on infants discharged home from neonatal care or deceased. Estimation of sex-specific PAD over time was based on infants discharged home exclusively. Analysis of in-hospital survival was performed for all VLBW infants. Results: In 4,336 of 4,499 VLBW infants admitted from 1978 to 2018 with complete data (96.4%), survival rates improved between 1978–1982 and 1993–1997 (70.8 vs. 88.3%; hazard ratio (HR) 0.20, 95% confidence interval 0.14, 0.30) and remained stable thereafter. Boys had consistently higher mortality rates than girls (15 vs. 12%, HR 1.23 [1.05, 1.45]). Nonsurviving boys died later compared to nonsurviving girls (adjusted mean survival time 23.0 [18.0, 27.9] vs. 20.7 [15.0, 26.3] days). LOHS and PAD assessed in 3,166 survivors displayed a continuous decrease over time (1978–1982 vs. 2013–2018: LOHS days 82.9 [79.3, 86.5] vs. 60.3 [58.4, 62.1] days); PAD 40.4 (39.9, 40.9) vs. 37.4 [37.1, 37.6] weeks). Girls had shorter LOHS than boys (69.4 [68.0, 70.8] vs. 73.0 [71.6, 74.4] days) and were discharged with lower PAD (38.6 [38.4, 38.8] vs. 39.2 [39.0, 39.4] weeks). Discussion/Conclusions: LOHS and PAD decreased over the last 40 years, while survival rates improved. Male sex was associated with longer LOHS, higher PAD, and higher mortality rates.