Relative birth weight in twins

A total of 579 sets of twins delivered in an obstetric population of 26,111 over a 10-year period were studied to reassess the veracity of the commonly held opinion that the first twin delivered is usually the heavier. Among the 579 sets of twins, 32 (5%) were of equal weight, while in 247 (42%) cases, twin I was heavier than twin II. In 235 (41%) cases, twin II was larger than twin I, in 65 (11%) the weight could not be compared. The mean birth weight of twin I was 2440 g, while that of twin II was 2410 (P greater than 0.05). Thus, even though twin I had the weight advantage more often than twin II, the difference is not statistically significant (t = 0.431).