BAKERSFIELD, Calif. -- Each year in the United States, about 6,000 babies are born with Down's syndrome -- a developmental disorder caused by the presence of an extra chromosome.

A new study from Denmark has suggested that routine screening for Down's syndrome could cut the number of affected infants in half.

In 2004, the country began offering pregnant women a few simple tests to assess their baby's risk for Down's. These included blood tests to look for certain proteins, an ultrasound and a risk assessment based on the mother's age.

If doctors suspected a problem, only then did the woman have more invasive screening, such as amniocentesis.

Researchers studied groups of about 65,000 babies born each year. They found that the number of babies born with Down's dropped from about 60 to roughly 30 cases per year after nationwide screening began.

In the U.S., Down's syndrome testing is common in older mothers.

However, some ethical experts question the morality of a mass-screening program. They worry it would lead more parents to terminate pregnancies affected by Down's syndrome.