Birth order and delivery interval: analysis of twin pair perinatal outcomes.
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To determine whether second-born twins (B) have higher morbidity and mortality than first-born twins (A), using a paired analysis.We conducted a retrospective analysis of birth certificates and fetal and infant death certificates for 5138 twin pairs selected from those born in Washington State from 1989 to 2001. Twin A was vertex and delivered vaginally. Pairs were not size-discordant (< 20%) and had no malformations. Matched-pair odds ratios were calculated.Twin B had more fetal distress (OR=6.0) and more low 5-min Apgar scores (OR=2.1) than Twin A, except at short delivery intervals. Pairs had relatively high rates of combined vaginal plus cesarean deliveries at delivery intervals 15 min.If prompt vaginal delivery of Twin B does not occur, the benefits of vaginal delivery for Twin A might not outweigh the risks of distress and low Apgar scores in Twin B and vaginal plus cesarean delivery for the mother.