Sex differences in outcomes of very low birthweight infants: the newborn male disadvantage

Objective-To determine the differences in short term outcome of very low bi rthweight infants attributable to sex. Methods-Boys and girls weighing 501-1500 g admitted to the 12 centres of th e National Institute of Child Health and Human Development Neonatal Researc h Network were compared. Maternal information and perinatal data were colle cted from hospital records. Infant outcome was recorded at discharge, at 12 0 days of age if the infant was still in hospital, or at death. Best obstet ric estimate based on the last menstrual period, standard obstetric factors , and ultrasound were used to assign gestational age in completed weeks. Da ta were collected on a cohort that included 3356 boys and 3382 girls, repre senting all inborn births from 1 May 1991 to 31 December 1993. Results-Mortality for boys was 22% and that for girls 15%. The prenatal and perinatal data indicate few differences between the sex groups, except tha t boys were less Likely to have been exposed to antenatal steroids (odds ra tio (OR) = 0.80) and were less stable after birth, as reflected in a higher percentage with lower Apgar scores at one and five minutes and the need fo r physical and pharmacological assistance. In particular, boys were more li kely to have been intubated (OR = 1.16) and to have received resuscitation medication (OR=1.40). Boys had a higher risk (OR > 1.00) for most adverse n eonatal outcomes. Although pulmonary morbidity predominated, intracranial h aemorrhage and urinary tract infection were also more common. Conclusions-Relative differences in short term morbidity and mortality pers ist between the sexes.