genetics and prenatal diagnosis

Last reviewed 01/2018

The main indication for chromosome analysis is a pregnancy that has been identified as being at risk of a cytogenetic disorder due to:

  • following a high risk screening result for Down's syndrome
  • abnormalities found on ultrasound scan
  • a previous chromosome abnormality
  • where a parent is known to carry a chromosome abnormality
  • advanced maternal age

Genetic studies on the foetus can be undertaken on amniotic fluid cultures (usually at about 15-16 weeks gestation), by chorionic villus sampling (CVS) (from 11 weeks gestation), or by foetal blood sampling (from 18 weeks gestation). Foetal urine and pleural effusions are also occasionally used.