Cerebral palsy in the surviving twin associated with infant death of the co-twin

Monozygotic twins are at greater risk of dying and of serious morbidity than dizygotic twins, and both are at greater risk than singletons. This is only partly explained by the higher proportion of low birthweight infants among twins.

To compare, in same sex and different sex twins, birth weight specific neonatal death rates and cerebral palsy prevalence rates in the surviving twin when the co-twin has died in infancy.

Analysis of birth and death registration data for same sex and different sex twins for England and Wales 1993-1995 where both were live births. Death certificates of all liveborn twins who died were obtained from the Office for National Statistics. A questionnaire was sent to the general practitioners of all surviving co-twins to determine if the child had any disability.

The neonatal death rate in same sex twins was 25.4 and in different sex twins 18.0 per 1000 live births (death rate difference 7.4; 95% confidence interval 4.7 to 10.1; p < 0.001). The higher neonatal death rate in same sex compared with different sex twins is attributable to the higher proportion of same sex twins with low birth weight. Prevalence of cerebral palsy in the low birthweight group (< 1000 g) was marginally higher in same sex (224 per 1000) than different sex (200 per 1000) twin survivors. In the birth weight group 1000-1999 g, same sex twin survivors were at a significantly higher risk of cerebral palsy than those of different sex: 167 v 21 per 1000; difference 145 (95% confidence interval 44 to 231; p < 0.01) per 1000 infant survivors.

There are two components to the cause of cerebral palsy in twins. Immaturity per se predisposes to cerebral damage. Also, same sex twins may sustain cerebral damage that is in excess of that due to immaturity.