title: "Masculinizing" effect on respiratory morbidity in girls from unlike-sex preterm twins: a possible transchorionic paracrine effect.
abstract: OBJECTIVE
  Preterm male infants are at a disadvantage when compared with female infants regarding the incidence of respiratory and neurologic morbidity and mortality. At term, female infants from unlike-sex twin pairs have birth weights that are closer to their male co-twins than to girls from like-sex twin pairs. We hypothesized that if the male disadvantage is mediated via factors that affect fetal lung development, there may be a potential effect on the incidence of respiratory distress syndrome and its complications in female infants from unlike-sex pairs.
  
  
  METHODS
  In this population-based study we used data from the Israel Neonatal Network, which included data from 8858 very low birth weight (500-1500 g) infants of 24 to 34 weeks' gestation. The incidence of morbidity and mortality was compared in male and female infants from singletons and like-sex and unlike-sex twin pairs. Multivariable analyses were used, accounting for relevant confounding variables.
  
  
  RESULTS
  Male singletons and like-sex twins were at increased risk for mortality, respiratory distress syndrome, pneumothorax, bronchopulmonary dysplasia, periventricular-intraventricular hemorrhage, and periventricular leukomalacia. However, in unlike-sex twin pairs, no difference was seen in the incidence of respiratory morbidity between male and female twins. The male disadvantage was maintained for mortality and periventricular-intraventricular hemorrhage.
  
  
  CONCLUSIONS
  These findings suggest that the difference in morbidity and mortality between male and female premature infants represents a male disadvantage as opposed to a female advantage and that this disadvantage may be transferred from boys to girls in unlike-sex twin pairs, perhaps via an intrauterine paracrine effect.
authors.affiliation: Department of Neonatology, Kaplan Medical Center, PO Box 1, Rehovot 76100, Israel. eric_s@clalit.org.il
authors.forename: Eric S
authors.initials: ES
authors.lastname: Shinwell
authors.forename: Brian
authors.initials: B
authors.lastname: Reichman
authors.forename: Liat
authors.initials: L
authors.lastname: Lerner-Geva
authors.forename: Valentina
authors.initials: V
authors.lastname: Boyko
authors.forename: Isaac
authors.initials: I
authors.lastname: Blickstein
mesh_terms: D001997:Bronchopulmonary Dysplasia / Q000453:epidemiology; D002543:Cerebral Hemorrhage / Q000453:epidemiology; D019992:Databases as Topic; D005260:Female; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D007234:Infant, Premature; D019102:Infant, Very Low Birth Weight; D007969:Leukomalacia, Periventricular / Q000453:epidemiology; D008297:Male; D015999:Multivariate Analysis; D019899:Paracrine Communication; D011030:Pneumothorax / Q000453:epidemiology; D012127:Respiratory Distress Syndrome, Newborn / Q000453:epidemiology*; D018570:Risk Assessment; D012737:Sex Factors; D014427:Twins