Sex differences in cardiorespiratory transition and surfactant composition following preterm birth in sheep

Male preterm infants are at greater risk of respiratory morbidity and mortality than females but mechanisms are poorly understood. Our objective was to identify the basis for the male disadvantage following preterm birth using an ovine model of preterm birth in which survival of females is greater than males. At 0.85 of term, fetal sheep underwent surgery (11 female, 10 male) for the implantation of vascular catheters to monitor blood gases and arterial pressure. After caesarean delivery at 0.90 of term, lambs were monitored for 4h while spontaneously breathing; lambs were then euthanized and static lung compliance measured. We analysed surfactant phospholipid composition in amniotic fluid and in bronchoalveolar lavage fluid (BALF) taken at necropsy; we also analysed surfactant protein (SP) expression in lung tissue. Before delivery male fetuses tended to have lower pH (p=0.052) compared to females. One hour after delivery, males had significantly lower pH and higher PaCO(2), lactate, glucose and mean arterial pressure than females. Two males died 1 hour after birth. Static lung compliance was 37 lower in males than females (p