First Trimester Screening for Chromosome Abnormalities
To determine the risk of certain chromosomal abnormalities, a combination of an ultrasound examination and a blood test can be done between the 11th and 13th weeks of pregnancy. This test, called an ultrascreen, combines a standard first-trimester ultrasound with a specialized measurement called a nuchal translucency. The blood specimen is analyzed for two chemicals, free Beta-hCG (human chorionic gonadotropin) and PAPP-A (pregnancy-associated plasma protein-A), which are normally found in the blood of all pregnant women. The results of the nuchal translucency and the blood test, when considered with the mother’s age, give a specific estimated risk for Down’s syndrome and Trisomy 18.