syndrome and Trisomy 18, but unlike the second-trimester screen, it does not include a screen for neural tube defects. The purpose of screening earlier (the test can be done between 10-14 weeks) is to provide at-risk individuals the opportunity to participate in additional testing such as amniocentesis or chorionic villus sampling earlier. This can help some couples in decision-making regarding the pregnancy.

Screening in the first-trimester involves both blood work and an ultrasound. Nuchal translucency (thickness of the fetal skin at the back of the neck) is measured by ultrasound. The level of 2 markers in the pregnant woman's blood is also measured, plasma protein-A and free beta-hCG. The combination of information from the ultrasound and blood work then is used to calculate the risk for Down syndrome and Trisomy 18.

First-trimester screening is a specialized test that is not universally performed at all offices and hospitals. For interested patients, referral to a university or specialized center may be necessary. Contact your obstetrician for further information.

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