What conditions does NIPT detect?

Standard NIPT screens for the three common trisomies — Down syndrome (trisomy 21), Edwards syndrome (trisomy 18) and Patau syndrome (trisomy 13). Many laboratories also screen for sex chromosome differences. What it does not detect is the more important half of the answer: Around half of the chromosome abnormalities that amniocentesis would find are not detected when only trisomies 21, 18 and 13 are screened. Broken down by age, about 75% are missed in women under 35 and about 43% in women over 35 — the difference reflects the fact that trisomies make up a larger share of abnormalities in older mothers. Unbalanced translocations, deletions and duplications are not detected. Single gene conditions — thalassaemia, cystic fibrosis, sickle cell disease and similar — are not screened at all. Open neural tube defects such as spina bifida are not screened. A separate blood test at 15 to 20 weeks covers these. Structural abnormalities are not detected. Ultrasound covers these. On expanded panels that claim to screen for microdeletions: ACMG states there is insufficient evidence to recommend routine screening for copy number variants other than 22q11.2 deletions. Current genome-wide screening is designed to detect variants larger than 7 megabases, while most clinically relevant ones are smaller. Treat these add-ons cautiously. A normal NIPT result reduces the chance of specific conditions. It does not mean a baby is free of all genetic conditions.