Second-Trimester Screening

A second-trimester screening occurs during the 15th and 21st weeks of pregnancy. It does not require an ultrasound. You will only need to have blood drawn, which will help determine if there are risks for certain genetic conditions or birth defects.

Cell-free fetal DNA testing

Fetal DNA testing can be done as early as 10 weeks. This method is used to screen for chromosomal abnormalities within the fetus. Blood and DNA samples will be extracted from both the mother and fetus to check for Down syndrome, trisomy 13 and trisomy 18, and sex chromosome abnormalities. This test has a 99% accuracy rate in detecting whether a mother is at risk of having a baby with a chromosomal disorder.

Unlike the first- and second-trimester screening, the fetal DNA test is recommended to women who have already determined they are at risk. This test is not recommended for women carrying more than one baby or those who have a low risk of having a baby with chromosomal disorders. Women who qualify for the test are those above the age of 35 or those with an abnormal screening test.

Because the test is more specific than the first- or second-trimester screening, the fetal DNA test is more accurate in determining chromosomal defects. However, the results will likely vary depending on the lab. If the test results are negative, which means there is no defect, your doctor will let you know if additional testing is necessary. If the results are positive, your doctor will work with you and your family to determine next steps.