Director, National Down Syndrome Cytogenetic Register
Wolfson Institute of Preventive Medicine
Barts and the London School of Medicine
Queen Mary, University of London
It is incorrect to report that more women are declining antenatal screening for Down’s syndrome because there has been a reported 4% increase in Down’s syndrome live births in England and Wales from 1989 to 2006 (717 and 749 affected births in the two years respectively).
Key results from the Register :
- It is correct that the numbers of Down’s syndrome live births in England and Wales increased by 4% from 1989 to 2006.
- Since 1989 there has been an increase in the age women become pregnant. For example in 1989 6% of pregnant women were over 35 years of age: by 2006 it was 15%.
- The risk of a Down’s syndrome pregnancy increases with maternal age, being 16 times greater for a 40 year old woman compared to a 25 year old woman.
- Due to the increase in the age women become pregnant, the number of Down’s Syndrome live births would have increased by over 50% from 1989 to 2006 if antenatal screening, diagnosis and subsequent terminations had not been available. There would have been an estimated 1454 Down’s syndrome live births in 2006 instead of 749 (see figure 1).
- Since 1989 the proportion of women having antenatal screening has increased; the number of antenatal diagnoses increased 3.5 fold whilst the number of diagnoses after birth has remained fairly constant (see figure 2).
- 92% of women who have an antenatal diagnosis of Down’s syndrome decide to have a termination of the pregnancy. This proportion has not changed since 1989.
- In summary : the effect of the increase in the age women have their babies on increasing the incidence of Down’s syndrome pregnancies is approximately balanced by the decrease in the birth prevalence due to a greater proportion of pregnant women being screened and having a termination of pregnancy.