ATLANTA – Down syndrome in the United States is more common than previously thought, at one case for every 733 live births, according to a new government report containing what are regarded as the most reliable estimates yet on the prevalence of 18 types of birth defects.
Previously, Down syndrome, a type of retardation caused by a genetic mutation, was estimated to occur in a range from one in every 800 live births to one in every 1,000.
The report, released Thursday by the Centers for Disease Control and Prevention, also found that cleft lip occurs in about one in every 1,000 births, and cleft palate in about one in every 1,500.
Advocacy groups that help families affected by birth defects celebrated the report. They noted that the new numbers are based on statewide data, while previous estimates were derived from selected clinics and hospitals.
“Until now, there’s been a real dearth of good, reliable, national statistics on Down syndrome,” said Suzanne Armstrong, spokeswoman for the National Down Syndrome Society.
The risk of Down syndrome increases with the age of the mother, from an estimated 1 in 2,000 among 20-year-old women to 1 in 100 for 40-year-old women. Many women are having babies later in life, which might explain the higher rate in the new study.
But because the new statistics were not collected in the same way as the old ones, it is not clear whether Down syndrome has really increased, Armstrong and others said.
The reported incidence of Down syndrome would be higher if not for abortions among women who decide to terminate their pregnancies after prenatal tests show the fetus has the chromosomal disorder.
The researchers included only 18 of the thousands of birth defects that doctors and scientists have identified. Missing are common birth defects such as clubfoot, hip dislocation and hypospadias, in which a boy’s urinary opening is on the underside of the penis instead of the tip. Spina bifida was not included because health officials already have what they consider reliable estimates.
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