First trimester scan
It is a test performed at 11-13 weeks of pregnancy that can identify more than 85% of babies with Down syndrome and trisomy 18. The screening involves
- Ultrasonographic measurement of nuchal translucency (a skin fold behind the neck). A positive result is not diagnostic but indicates that an increased risk for a problem exists and that additional testing should be considered.
- Chorionic villous sampling in week 13 which is taking a sample of the chorionic villi of the placenta for genetic analysis under the guidance of ultrasound machines for safety.
Second trimester scan
It is a test performed at 14-17 weeks of pregnancy that can identify more than 85% of genetic abnormalities. The screening involves
- Biochemical analysis of maternal serum levels of beta-hCG (From the placenta), Free Estriol (From the fetus and placenta) and alphafeto protein (From the fetus)
- Ultrasound anomaly scan at 18-21 weeks
- Amniocentesis: It is performed at 16-20 weeks and it consists of a study of amniotic fluid after taking a sample of it by an aspiration needle guided through the abdomen by ultrasound to choose the safest and best location for aspiration.