Screening for the main chromosomal conditions in the baby from a blood sample taken from the mother.
From week 10 of pregnancy, the mother's blood carries fragments of DNA from the placenta. Analysing them estimates the risk of trisomies 21, 18 and 13, among others.
It is a highly reliable screening test, but not a diagnostic one: if the result is abnormal, it is confirmed with an invasive test before any decision is made. I explain everything calmly, before and after.