Dr. Peter Boylan:

It depends on the complexity of the problem. For example, some congenital heart anomalies are not detectable until around 18 to 20 weeks when a detailed ultrasound scan is done. It is worth noting that only about 50% of all congenital abnormalities of the heart are diagnosed antenatally. That is a universal figure, no matter how good the scanning is, so there are problems in that respect.

We can diagnose conditions such as anencephaly very early on in pregnancy, but sometimes more complex problems are not apparent. However, certainly by 20 weeks, we should have been able to diagnose the most obvious or the severe ones. It is not always possible though and there is often a bit of uncertainty about the outlook in a condition, and women are followed throughout the pregnancy when there is an abnormality and they are continuing on with the pregnancy.