title: Twinning and cerebral palsy: experience in four northern California counties, births 1983 through 1985.
abstract: BACKGROUND
  Twinning is associated with heightened risk of cerebral palsy (CP) and is increasing in the United States and elsewhere.
  
  
  METHODS
  Twins with moderate or severe congenital CP were identified in a cohort of 155,572 children born 1983 through 1985 in four northern California counties and surviving to 3 years. The prevalence of CP in twins and factors associated with increase in risk were examined.
  
  
  RESULTS
  Among 2985 twins, 20 children in 18 pairs had CP. The prevalence of CP was 6.7 per thousand 3-year-old twin children (95% confidence interval [CI], 4.2 to 11), 12 per thousand twin pregnancies (95% CI, 7.2 to 19), and 1.1 per thousand singletons (95% CI, 0.97 to 1.3). Ten percent of all CP was in twins; 22% of CP in infants of less than 1500 g birth weight occurred in twins. Twins were over-represented among very low birth weight infants but their risk of CP was comparable with that of very low birth weight singletons. Twins born weighing 2500 g and more had a CP risk 3.6 times that of singletons of similar weight. In children who survived fetal death of a co-twin, CP was 108 times more prevalent (95% CI, 42 to 273) than in singletons and 13 times more prevalent (95% CI, 4.5 to 37) than in twins whose co-twin was born alive. The CP rate in unlike-sex pairs was 13 per thousand (95% CI, 4.8 to 32), not significantly different from 11 per thousand (95% CI, 5.7 to 19) for like-sex pairs.
  
  
  CONCLUSIONS
  Twin pregnancies produced a child with CP 12 times more often than singleton pregnancies. The heightened risk was largely related to the tendency of twins to be low in birth weight and to a greater risk of CP in twins of normal birth weight compared with singletons of similar weight. Twins of unlike-sex pairs, necessarily dizygotic, were not at lower risk than like-sex pairs. The current increase in multiple births is likely to contribute more children with CP.
authors.affiliation: California Dept of Health Services, California Birth Defects Monitoring Program, Emeryville 94608.
authors.forename: J K
authors.initials: JK
authors.lastname: Grether
authors.forename: K B
authors.initials: KB
authors.lastname: Nelson
authors.forename: S K
authors.initials: SK
authors.lastname: Cummins
mesh_terms: D002140:California / Q000453:epidemiology; D002547:Cerebral Palsy / Q000151:congenital / Q000453:epidemiology*; D004200:Diseases in Twins; D005260:Female; D006801:Humans; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D008297:Male; D012306:Risk