Relative birth weights in twins

To determine if the first twin (Twin I) weighs more than the second twin (Twin II). One hundred and seventeen sets of twins delivered at the Federal Medical Centre Makurdi, Nigeria over a three year period between 1st January, 2005 and 31st December2007 were reviewed. Of the 117 sets of twins in the study, 9 (7.7%) were of equal weights while in 57 (48.7%) sets Twin I were heavier than Twin II. In 51 (43.6%) sets Twin II were heavier than Twin I. The mean birth weight of Twin I was 2.460 +/- 0.436 Kg while that of Twin II was 2.390 +/- 0.451 Kg, (P< 0.05). Twin I was often heavier than twin II. The difference in the mean birth weight of twin I and Twin II was statistically significant in favour of Twin I.