More British women are learning that their babies will have Down syndrome, but with 9 in 10 terminating their pregnancies the number of children born with the chromosomal disorder is steady, new research shows.

Down syndrome diagnoses are up by 71 percent since 1989, according to research published Tuesday in the British Medical Journal. The reason: women are waiting to have children. That’s significant because the odds of having a baby with Down syndrome increase from 1 in 940 for a mother who is 30 to 1 in 85 for a mother who is 40.

Meanwhile, prenatal screening for the disorder has become more advanced and more women are opting to do such testing in utero. Of couples who learn prenatally that their child will have Down syndrome, 92 percent decide to terminate the pregnancy.

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“What we’re seeing here is a steep rise in pregnancies with Down syndrome but that is being offset by improvements in screening,”said Joan Morris, a professor of medical statistics at Queen Mary, University of London who authored the study. “It was thought that these improvements would lead to a decrease in the number of births with Down syndrome. However due to increases in maternal age this has not occurred.”

Today, about 750 babies are born each year in Britain with Down syndrome.