Twins are at higher risk of CP than a baby born singly (singletons). Triplets and quadruplets are at even higher risk. For every thousand singleton births, about two have CP. For every thousand twin births, seven to ten have CP. And for triplets, about twenty to forty in every thousand have CP. Thus twins have about four times the risk of CP as singletons. Twinning is on the increase, mostly because of infertility treatments. In Europe, twins accounted for 4% of CP thirty years ago, but now account for about 10% of CP.
What puts twins at higher risk?
Most important is that twins are much more likely to be born prematurely (more than 3 weeks before the due date). In the USA in 2002, birth was premature for 10% of singletons but 58% of twins. Even when born at term (around the due date), twins tend to be smaller than singletons. Premature birth is a very important risk factor for CP, and being born small at term is also a risk factor. Therefore twins are generally born with one important risk factor for CP.
Is there anything that puts one set of twins more at risk than other twins?
Clearly, twins born more prematurely than other twins are at higher risk of CP. But another risk factor is their difference in weight. A recent study found that if one twin weighs more than 20% more than the other, both twins – the smaller and bigger - are at about 40% higher risk of CP. It does not seem to matter to risk of CP whether twins are of the same sex, or are a boy and a girl.
Is there anything that puts one twin in a pair more at risk than the other twin?
Being born first, or being the smaller or larger of twins, does not change the risk of CP. However, a boy twin is at about 30% higher risk for CP than a girl twin (singleton boys are also at slightly higher risk of CP than singleton girls, but the difference is not as large). Two important factors - death or CP in one twin - greatly increase the risk of CP in the other twin. If one twin was stillborn or died in the newborn period, the risk of CP in the other twin is about 5%, or nearly 7 times the risk when both twins survive. If one twin has CP, the other twin has about a 10% risk of also having CP, which is 10 - 15 times the overall risk for twins. However, this means that 90% of the time, just one of a pair of twins has CP. Considering that both twins have experienced the same pregnancy, and are delivered and cared for in the same hospital, it is perhaps surprising that we so often encounter just one member of a twin pair who is affected by CP.
Is there anything different about CP in twins than in singletons?
Twins tend to have pretty much the same types of CP, the same ranges of severity, and the same risk of associated problems as do singletons with CP.
FURTHER READING:
The National Library of Medicine maintains a free internet service that allows you to find the summaries of articles published in the medical literature going back to 1976. sometimes you can download the entire article.
Yokoyama Y, Shimizu T, Hayakawa K: Prevalence of cerebal palsy in twins, triplets and quadruplets. International Journal of Epidemiology 1995; 24: 943-948.
Pharaoh PO, Cooke T: Cerebral palsy and multiple births. Archives of Diseases in Childhood Fetal and Neonatal Edition. 1996; 75: F174-177.
Blickstein I: Cerebral palsy in multifoetal pregnancies. Developmental Medicine and Child Neurology 2002; 44: 352-355
Scher AI, Petterson B, Blair E et al: The risk of mortality or cerebral palsy in twins: a collaborative population-based study. Pediatric Research. 2002; 52: 671-681
Topp M, Huusom LD, Langhoff-Roos J et al: Multiple birth and cerebral palsy in Europe: a multicenter study. Acta Obstetricia et Gynecologica Scandinavica. 2004; 83: 548-553.