title: Fetal sex pairing and adverse perinatal outcomes in twin gestations.
abstract: OBJECTIVE
  To assess the association between fetal sex pairing in twin pregnancies and adverse perinatal and infant outcomes.
  
  
  METHODS
  A retrospective cohort study of 9770 infants from 4885 twin pregnancies delivered in 2007 was conducted with a statewide hospital discharge database for Texas. Log-binomial regression models based on generalized estimating equations were used to calculate relative risks (RR) and 95% confidence intervals (95% CI) for the following dichotomous outcomes: breech presentation, hospital mortality, intrauterine growth restriction (IUGR), low birth weight, prolonged length of stay (>4 days), receipt of mechanical ventilation, and respiratory distress syndrome (RDS).
  
  
  RESULTS
  The sample was composed of 4918 females and 4852 males. An approximately equal number of infants were from a female-female pregnancy (n = 3270), mixed-sex pregnancy (n = 3296), and a male-male pregnancy (n = 3204). Twins of either sex from mixed-sex pairs were 45% less likely to die in the hospital compared with females from a female-female pregnancy (RR, 0.55, 95% CI, 0.31-0.98). Males from a male-male pair were 33% less likely than females from female-female pairs to experience IUGR (RR, 0.67; 95% CI, 0.53-0.83). The incidence of RDS was significantly increased in males from male-male twin pairs versus females from female-female pairs (RR, 1.21; 95% CI, 1.05-1.41).
  
  
  CONCLUSIONS
  Male infants from male-male twin pairs were more likely to develop RDS and be placed on a ventilator but less likely to experience IUGR than female infants from female-female pairs.
authors.affiliation: Department of Obstetrics and Gynecology, Paul L Foster School of Medicine, Texas Tech University Health Sciences Center, El Paso, El Paso, TX 79905, USA. zuber.mulla@ttuhsc.edu
authors.forename: Zuber D
authors.initials: ZD
authors.lastname: Mulla
authors.forename: Sanja Kupesic
authors.initials: SK
authors.lastname: Plavsic
authors.forename: Melchor
authors.initials: M
authors.lastname: Ortiz
authors.forename: Bahij S
authors.initials: BS
authors.lastname: Nuwayhid
authors.forename: Cande V
authors.initials: CV
authors.lastname: Ananth
mesh_terms: D001946:Breech Presentation / Q000453:epidemiology; D005260:Female; D005317:Fetal Growth Retardation / Q000453:epidemiology / Q000503:physiopathology; D005865:Gestational Age; D017052:Hospital Mortality; D006801:Humans; D007226:Infant Mortality; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D007234:Infant, Premature; D007902:Length of Stay; D016015:Logistic Models; D008297:Male; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology*; D059285:Pregnancy, Twin / Q000706:statistics & numerical data*; D012127:Respiratory Distress Syndrome, Newborn / Q000453:epidemiology / Q000503:physiopathology; D012189:Retrospective Studies; D012307:Risk Factors; D012727:Sex Characteristics; D013781:Texas / Q000453:epidemiology; D014427:Twins