What is Down syndrome screening for pregnant women?

Prenatal Down syndrome screening is a routine prenatal screening test used to assess the risk of the fetus having Down syndrome. Down syndrome is a common chromosomal abnormality that typically causes intellectual disabilities and specific physical characteristics. The screening is usually performed between weeks 11 and 20 of pregnancy, and evaluates risk by combining blood tests and ultrasound examinations. The blood test measures two or three specific maternal serum markers, such as progesterone, human chorionic gonadotropin (hCG), and free beta-hCG levels. The ultrasound examination measures the thickness of the fetal nuchal translucency (NT), which is a sonographic marker potentially associated with Down syndrome. The screening results provide a risk ratio indicating the likelihood of the fetus having Down syndrome. If the results indicate a high risk, doctors may recommend further diagnostic tests, such as amniocentesis or chorionic villus sampling (CVS), which can provide more definitive diagnostic information but also carry a certain risk of miscarriage. It is important to note that this screening is not a diagnostic tool, but rather a risk assessment method. Therefore, even if the screening result is positive, it does not mean that the fetus definitely has Down syndrome.