This test can be done when your pregnancy is between 11-13.5 weeks gestation (with the optimal time around 13 weeks) and it involves assessing the baby with ultrasound and taking measurements. These are entered into software developed by the Fetal Medicine Foundation along with the mother’s age and the results of the associated blood test. This program then allows us to calculate an individual risk of chromosomal abnormalities for each pregnancy.

This test is a risk assessment. It does not tell us which pregnancies are affected by chromosomal abnormalities. Approximately 5% of pregnancies will return as high risk and most of these will be normal, just as low risk does not entirely exclude an abnormality.

This screening method will detect approximately 88-93% of affected pregnancies.