Table 2

Stillbirth/live birth twin pairs: infant mortality among live births, England and Wales 1982–91

	No of live births	No of neonatal deaths (per 1000 live births)	No of postneonatal deaths (per 1000 live births)	No of infant deaths (per 1000 live births)
a Same sex	1294	81 (62.6)	21 (16.2)	102 (78.8)
b Different sex	402	13 (32.3)	7 (17.4)	20 (49.8)
a+b Total twin pairs	1696	94 (55.4)	28 (16.5)	122 (71.9)
a−b 2-150Monozygotic pairs	892	68 (76.2)	14 (15.7)	82 (91.9)
2b2-152Dizygotic pairs	804	26 (32.3)	14 (17.4)	40 (49.8)

↵2-150 Applying the Weinberg rule that, among dizygotic twins, there are an equal number of same sex as different sex pairs.
↵2-152 Based on the assumption that the number of infant deaths in different (dizygotic) sex pairs is the same as in same dizygotic sex pairs.