New Delhi, Oct 29 (IANS): The increasing trend of late marriages and delayed first pregnancy raises the risk of babies being born with Down's syndrome, a study revealed Wednesday.

Conducted by pathology specialist Metropolis Healthcare Ltd, close to 40,000 prenatal screenings - which help in revealing the disorder in the foetus - were processed for the study.

Of the 2,996 mothers aged between 35 and 40 years, 21.89 percent tested positive for Down's syndrome during pregnancy, while 7.78 percent of the 9,965 mothers aged between 31 and 35 years had the risk, the survey said.

Deepak Sanghavi, head of the department of clinical chemistry and accession at Metropolis Healthcare Ltd, said: "With the increase in the maternal age, the likelihood of having a child affected with Down's syndrome increases considerably."

"A woman who is 40 years old at the time of conceiving a child is at 16 times greater risk of giving birth to a baby affected with Down's syndrome, compared to a woman who conceives at the age of 25," he added.

Down's syndrome is a genetic disorder that causes mental retardation and abnormal physical growth among children and occurs when an individual has a full or partial extra copy of chromosome 21.

It increases the risk of congenital heart defects, respiratory, hearing problems, childhood leukemia, and thyroid conditions and affects about one in 800 babies worldwide. In India, every year, more than 23,000 babies are born with Down's syndrome.

October is observed as Down's syndrome awareness month globally.