title: Perinatal mortality in term and preterm twin and singleton births.
abstract: Although, in general, twins have higher perinatal mortality rates than singletons, preterm twins have lower perinatal mortality rates than singletons of the same birth weight or gestational age. This study investigated the hypotheses that this paradoxical twin advantage: 1) is due to gestational age distribution differences between the singleton and twin populations, and 2) is due to increased likelihood of birth having occurred in a tertiary perinatal center. A pre-existing, time-limited data set of all births in the province of Ontario in odd years between 1979 and 1985 was chosen for this study because of the large sample size (n = 618,579). Multivariable logistic regression of the relationship between perinatal mortality and twin status was controlled for mother's age, hospital level and gestational age. Findings confirm the lower mortality of preterm twins. After controlling for level of hospital of birth this difference remained, suggesting that level of hospital of birth was not a major factor responsible for the twin advantage. Analyses in which gestational age was standardized indicate that, for those whose gestational age was less than 2 SD below the mean for their particular group (twin or singleton), twins were actually at higher risk than singletons. These results support hypothesis 1 and do not strongly support hypothesis 2. The results also support earlier authors' suggestions that the definition of term birth should be different for twins and singletons
authors.affiliation: Surveillance and Risk Assessment Division, Centre for Chronic Disease Prevention and Control, Health Canada, Ottawa, Ontario, Canada.
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Payne
authors.forename: M Karen
authors.initials: MK
authors.lastname: Campbell
authors.forename: Orlando
authors.initials: O
authors.lastname: DaSilva
authors.forename: John
authors.initials: J
authors.lastname: Koval
mesh_terms: D005865:Gestational Age; D006761:Hospitals; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D007234:Infant, Premature; D016015:Logistic Models; D015999:Multivariate Analysis; D016017:Odds Ratio; D012307:Risk Factors; D014427:Twins