title: Relationship of mode of conception and sex concordance with mortality/morbidity in preterm twins.
abstract: OBJECTIVE
  To assess the association of mode of conception and sex concordance with neonatal outcomes in very preterm twins.
  
  
  METHODS
  Twin pairs born at gestational age ≤ 32 weeks and admitted to a Level 3 neonatal intensive care unit (NICU) in 2010-2011 were retrospectively identified from the Canadian Neonatal Network™ database. A composite outcome representing neonatal mortality or any severe morbidity (intraventricular hemorrhage grades ≥ 3 or periventricular leukomalacia, retinopathy of prematurity stages ≥ 3, bronchopulmonary dysplasia, or necrotizing enterocolitis stages ≥ 2) was compared between twins conceived using assisted reproduction technologies (ARTs) or spontaneously (SP), and tested for association with sex concordance in individual-level and pair-wise multivariable logistic regression analyses.
  
  
  RESULTS
  Study subjects included 1,508 twins from 216 ART (53 [25%] male-male, 104 [48%] male-female, and 59 [27%] female-female) and 538 SP (192 [36%] male-male, 123 [23%] male-female, and 223 [41%] female-female) pairs. No statistically significant association was detected between mode of conception and the composite outcome of mortality/morbidities. The composite outcome was significantly higher in same-sex than in opposite-sex twins (OR = 1.68; 95% CI = [1.09, 2.59]). This relationship was most pronounced in ART pairs (OR = 2.25; 95% CI = [1.02, 4.98]), with increased rates in one or both twins from male-male versus opposite-sex ART pairs (OR = 3.0; 95% CI = [1.07, 8.36]).
  
  
  CONCLUSIONS
  Same-sex pairing was associated with higher mortality/morbidities in very preterm twins admitted to the NICU, and can be used in clinical practice to identify twins at higher risk of adverse neonatal outcomes.
authors.affiliation: Maternal-Infant Care Research Centre, Mount Sinai Hospital, Toronto, Ontario, Canada.
authors.forename: Lucia
authors.initials: L
authors.lastname: Mirea
authors.forename: Junmin
authors.initials: J
authors.lastname: Yang
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Paterson
authors.forename: Vibhuti
authors.initials: V
authors.lastname: Shah
authors.forename: Kate L
authors.initials: KL
authors.lastname: Bassil
authors.forename: Shoo K
authors.initials: SK
authors.lastname: Lee
authors.forename: Prakesh S
authors.initials: PS
authors.lastname: Shah
mesh_terms: D001997:Bronchopulmonary Dysplasia; D002170:Canada; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D014427:Twins