What prenatal test can be used to screen for Down syndrome during the first trimester?

During the first trimester, a combination of a maternal blood test and ultrasound is the standard approach for screening for Down syndrome. This is often referred to as the first-trimester screening, which typically involves measuring specific substances in the mother's blood, along with an ultrasound assessment to check for nuchal translucency—a fluid collection at the back of the baby's neck. An increased amount of nuchal translucency can indicate a higher risk of Down syndrome or other chromosomal abnormalities.

The blood test usually measures levels of pregnancy-associated plasma protein A (PAPP-A) and human chorionic gonadotropin (hCG). When the results of these tests are combined with the ultrasound findings, healthcare providers can calculate the risk of the fetus having Down syndrome, allowing for informed decision-making and discussions about further testing if needed.

In contrast, amniocentesis and chorionic villus sampling (CVS) are more invasive procedures used for definitive diagnosis of genetic conditions, including Down syndrome, but they are not typically performed in the first trimester for screening purposes. A complete blood count does not provide any information related to genetic conditions.