Objective: To compare the perinatal outcome of the presenting twin to its co-twin.
Study design: All live nonanomalous twin gestations delivered at >25 weeks' gestation between 1984 and 1994 (N=461) were identified. Twin A was compared to twin B regarding the following variables: presentation, Apgar score (AS) <4 at 1 minute, AS <7 at 5 minutes, birth weight, gender, traumatic delivery, meconium-stained amniotic fluid, cord prolapse, need for mechanical ventilation, intraventricular hemorrhage, respiratory distress syndrome, sepsis, seizures, perinatal mortality, and length of nursery stay.
Results: Except for differences in presentation, the perinatal outcome was similar in both twins regarding variables studied. This continued to hold true after subdividing according to mode of delivery, when infants with birth weight < or = 1500 g were considered separately, and when vaginally delivered cephalic twin A was compared to the noncephalic co-twin. However, differences in some outcome variables became evident when pregnancies with only one affected member were analyzed separately.
Conclusions: When all twin pairs are considered, the outcome of the second-born twin is similar to that of the first-born regardless of the mode of delivery, presentation, or birth weight < or = 1500 g. If only those twin pairs with one affected and one unaffected twin are considered, it becomes apparent that the presenting twin is at increased risk for infection-related morbidities whereas the co-twin is at risk for other complications.