Down Syndrome Cases Rise as Women Delay Pregnancy
A study conducted at Queen Mary, University of London finds that the number of Down syndrome pregnancies has risen dramatically over the past two decades. The research results, which are published in the British Medical Journal, notes that a major factor is that many women are choosing to delay pregnancy.
Down syndrome is the most commonly occurring chromosomal condition. Approximately one in every 733 infants is born with the syndrome. Down syndrome occurs when an individual has three rather than two copies of the 21st chromosome. Down syndrome can affect people of all races, but the incidence increases with the age of the mother. Individuals who have Down syndrome have an increased risk for certain medical conditions, such as heart defects, childhood leukemia, thyroid conditions, respiratory problems, and hearing disorders.
The study’s authors based their research on data from the National Down Syndrome Cytogenetic Register, a resource housed at Queen Mary, University of London, which has kept records of nearly all cases of Down syndrome pregnancies and births in England and Wales since 1989. The researchers noted that although the number of Down syndrome pregnancies has increased, so has the number of women being screened for the disorder. There have also been major improvements in prenatal screening.
In a release issued by Queen Mary, University of London, Joan Morris, Professor of Medical Statistics at the university, explained that the sharp increase in pregnancies with Down syndrome is being offset by improvements in prenatal screening. “It was thought that these improvements would lead to a decrease in the number of births with Down’s syndrome. However due to increases in maternal age this has not occurred.”
Morris also noted that the wider availability of Down syndrome screening tests over the past 20 years has meant that clinicians are identifying more cases. Analysis of the data shows a 71 percent increase in the number of Down syndrome pregnancies and births which researchers believe is mainly the result of women delaying their decision to have children. The risk of having an infant with Down syndrome is one in 940 for women age 30, but increases dramatically to one in 85 by age 40.
The researchers reported a significant increase in the proportion of Down syndrome pregnancies in women younger than 37 being detected by screening, rising from 3 percent to 43 percent, although the number has remained around 70 percent for older women. This reflects the improvements made in prenatal screening, especially for younger women. Another number that has not changed is the proportion of couples who decide to terminate a Down syndrome pregnancy, which has been constant at 92 percent. Without terminations, the increase in the age of women becoming pregnant would have led to a rise of 48 percent in the number of births of children with Down syndrome, according to the study.
Morris J and Alberman E. British Medical Journal 2009:339
National Down Syndrome Society
Queen Mary, University of London release, October 27, 2009