Cerebral palsy in twins: a national study.
BACKGROUND
Cerebral palsy is more common in twins than singletons. Among twins, if one twin suffers a fetal death or dies in infancy, the prevalence of cerebral palsy in the surviving co-twin is considerably increased, and those from like-sex pairs are particularly at high risk.


OBJECTIVE
To compare birthweight specific cerebral palsy prevalence in like-sex and unlike-sex twins where both twins survive infancy and to provide a comparative and composite picture of cerebral palsy prevalence according to whether a co-twin died or where both twins survived.


METHODS
Parents of twins born in England and Wales in 1994 and 1995 completed a booklet with open ended questions asking whether their twins had any medical, physical, visual, genetic, or chromosomal problems. Any mention of cerebral palsy, hemiplegia, diplegia, or quadriplegia allowed the child to be included as a case of cerebral palsy. Birthweight specific prevalence rates of cerebral palsy were determined for like and unlike-sex twins in birthweight groups < 1000 g, 1000-1499 g, 1500-1999 g, 2000-2499 g, and > or = 2500 g.


RESULTS
When both twins survived infancy, like-sex were at greater risk of cerebral palsy than unlike-sex twins, but the difference was not statistically significant. If both twins survived infancy, the birthweight specific prevalence of cerebral palsy was significantly less than if the co-twin had died.


CONCLUSIONS
Among the generality of twins, like-sex compared with unlike-sex twins are at greater risk of cerebral palsy particularly if one twin suffers a fetal or infant death. Although it is not possible to subdivide the twins according to zygosity, it is postulated that monozygosity and, specifically, monochorionicity may be the crucial feature that leads to the higher prevalence of cerebral impairment among like-sex twins.
Department of Public Health, University of Liverpool, Liverpool L69 3GB, UK. p.o.d.pharoah@liv.ac.uk
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D001724:Birth Weight; D002547:Cerebral Palsy / Q000453:epidemiology*; D004200:Diseases in Twins / Q000453:epidemiology*; D004739:England / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D015995:Prevalence; D012307:Risk Factors; D012737:Sex Factors; D014852:Wales / Q000453:epidemiology