The number of such births in the country rose to 89 out of 82,164 births from 40 out of 71,848 over the period, the figures show.
The results are only partly due to women in Switzerland having children at an older age, gynecologist Daniel Surbek told the ATS news agency.
Surbek, chief doctor at the university hospital of Bern, said a growing number of women either refuse to have a prenatal diagnosis or they decide to accept having the child despite a positive test for Down’s syndrome, a genetic disorder caused by a chromosome abnormality.
The probability of a pregnant woman having a child with Down’s syndrome increases sharply with age.
At 25, the likelihood is one in 1,300.
At the age of 40, the odds drop to one in 100, while at 46, one in 20 children are at risk of being born with Down’s syndrome.
Also known as trisomy 21, it usually results in mental impairment, stunted growth and various associated health problems.
Surbek said he was personally astonished by the number of women who, despite receiving detailed explanations, decline to have prenatal testing for the syndrome.
No statistics, however, are available to show how such many cases occur in Switzerland.
Since 2012, new tests have been available in Swiss hospitals, allowing for a diagnosis of the child through samples of the mother’s blood.
The tests are more accurate and less invasive than amniocentesis, a medical procedure that involves inserting a needle to withdraw amniotic fluid around the fetus that is examined under a microscope for potential chromosome abnormalities.
The impact of the new tests has yet to be reflected in the statistics.
“I start with the principle that with these new tests the number of children with Down’s syndrome is going to stabilize, even drop a little,” Surbek told ATS.
Between 75 and 90 percent of women confronted with a diagnosis of the syndrome decide to have an abortion, the news agency said.
This only represents a tiny fraction of the number of abortions in Switzerland, the federal statistics office says.
Only 5.5 percent of all abortions are linked to the health of either the mother or the child, the office said.