Study Links Twin Births to Cerebral Palsy

For release: Wednesday, December 08, 1993

The current rise in multiple births may contribute to an increase in children born with cerebral palsy (CP), according to a report published in the December issue of Pediatrics .* In a study involving more than 155,000 children, researchers from the National Institute of Neurological Disorders and Stroke (NINDS) and the California Birth Defects Monitoring Program (CBDMP) found that twin pregnancies produced a child with CP more than 10 times as often as pregnancies producing a single child.

"With the number of twin births on the rise in this country and others, it is vital for us to increase our base of scientific knowledge about this very special population," said Patricia A. Grady, Ph.D., acting director of the NINDS. "Twins accounted for 10 percent of all cases of CP in this study, and we need to explore the reasons behind that number."

CP refers to a group of disorders with different causes that affect motor-control areas of the central nervous system. Its symptoms include movement disorders and often problems in speech and learning, as well as delays in physical development, and sometimes seizures. About half a million Americans have CP and an estimated 5,000 new cases of disabling congenital CP are added to the American population each year.

The current study was led by Judith K. Grether, Ph.D., an epidemiologist with the CBDMP, a division of the California Department of Health Services, and by Karin B. Nelson, M.D., acting chief of the NINDS Neuroepidemiology Branch. They examined 2,985 individuals from 1,537 twin pairs who were born between 1983 and 1985 in four northern California counties and who survived to age three. The researchers found that among the almost 3,000 children from twin pairs, 20 children in 18 pairs had CP. Approximately seven out of every one thousand twin children had moderate or severe CP. And, more than 10 twin pairs out of every thousand twin pregnancies had CP in one or both members.

One possible explanation offered by the researchers is that twins are often born with a low birth weight (less than 2,500 grams, or 5 1/2 pounds) which is strongly associated with CP. The authors reported that the risk of CP in low birth weight twins was similar to the risk of CP in single children of low birth weight. However, twins who were born at a normal birth weight (more than 2,500 grams) were shown to be at an increased risk of CP, more than three and one half times that of single children born at normal birth weight.

Another finding in the study was that twins who survived a fetal death of their co-twin were 108 times more likely to have CP than single children and 13 times more likely than twins whose co-twin survived. Three out of four of these children were from identical twin sets and were normal or nearly normal in birth weight. The risk of CP was similar in twins of like gender or unlike gender pairings.

Although the results reported in Pediatrics describe a fairly small number of twins, the findings were replicated by a study conducted in Western Australia which extended the research to triplets. That study, published last month in the British Medical Journal, reported that twin pregnancies produced a child with CP 8 times more often than single pregnancies, while in triplet pregnancies a child with CP was produced 47 times more often. Again, scientists found that the death of one infant in a multiple set is related to a high risk of CP in the survivor(s).

Dr. Nelson, a co-author of both studies, said: "We have always known that low birth weight babies were at higher risk for neurological disorders, but the new results of these studies demonstrate how substantial the risks are for children of multiple births."

The number of twin births and, as a result, low birth weight babies, has climbed sharply in the past few decades. The Pediatrics article points out that medical science has been "strikingly successful" in allowing low birth weight infants to survive but "not effective in preventing their low birth weight or altering the rate of neurological morbidity among them." Subsequently, many more healthy infants survive, but there is also an increase in the number of infants with long-term neurological disability. The authors say that many of the findings were unexpected, because previous studies predated modern neonatal and obstetrical care and were not based on such well-defined populations.

The NINDS, one of the National Institutes of Health located in Bethesda, Md., is the nation's principal supporter of research on the brain and nervous system, including cerebral palsy. The Institute is a lead agency for the Congressionally designated Decade of the Brain.

*Judith K. Grether, Ph.D.; Karin B. Nelson, M.D.; and Susan K. Cummins, M.D. "Twinning and Cerebral Palsy: Experience in Four Northern California Counties, Births 1983 Through 1985." Pediatrics, December, 1993, Vol. 92, Number 6, pp. 854-858.

Date Last Modified: Tuesday, March 08, 2005

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