Table 1

Comparison of neonatal mortality in same sex and different sex twins: England & Wales 1993–1995

Birth weightSame sexDifferent sexSame − different sex difference in neonatal death rate (95% CI); p valueEstimated proportion of monozygotic twins (%)
Number of
live births
Number of neonatal deathsNeonatal death rate/1000Number of
live births
Number of neonatal deathsNeonatal death rate/1000
Not stated8296376.03922666.39.7 (−23.5 to +38.7); 0.0635.8
<500 g9978787.93227843.8−55.9 (−186.6 to +120.7); 0.551.1
500–999 g942432458.6366131357.9100.6 (41.2 to 158.1); <0.00144.0
1000–1499 g1 90212967.87215677.7−9.8 (−34.0 to +11.4); 0.345.0
1500–1999 g4 5674910.71 929178.81.9 (−3.9 to +6.7); 0.540.6
2000–2499 g9 707363.74 472112.51.2 (−0.9 to +3.1); 0.236.9
2500–2999 g10 855272.55 601101.80.7 (−1.0 to +2.1); 0.431.9
3000–3499 g3 912123.12 28052.20.9 (−2.3 to +3.5); 0.526.4
⩾3500 g5402240.7333721.019.7 (−5.5 to +43.1); 0.123.7
Total33 35384825.416 12629018.07.4 (4.7 to 10.1); <0.000134.8