Prenatal Testing

Here’s an in-depth look at the screening and diagnostic tests you might undergo, and how some real couples dealt with the decisions and emotional issues involved.

blood work
This is usually done at your first prenatal appointment to screen for certain diseases, including STDs, and determine your blood type.

chorionic villus sampling (CVS)

WHO IT’S OFFERED TO:
Women who will be older than 35 at delivery; those who have an abnormal first-trimester screening
test result.

WHEN IT’S OFFERED: At 10 to 12 weeks.

WHAT IT SCREENS FOR:
Down syndrome and some other chromosomal defects.

HOW IT WORKS: A small piece of tissue is taken from the placenta via a tube inserted through the cervix or a needle inserted through the uterine wall.

HOW EFFECTIVE IT IS: Almost 100 percent. It poses a miscarriage risk of approximately 1 percent.

WHAT IF …? If a defect is diagnosed, you’ll need to decide whether to continue the pregnancy.

first-trimester screening

WHO IT’S OFFERED TO: All women.

WHEN IT’S OFFERED: At 10 to 13 weeks.

WHAT IT SCREENS FOR: Chromosomal defects such as Down syndrome and trisomy 18 (an often lethal defect); some cardiac defects.

HOW IT WORKS: Blood is drawn from the mother, and three fetal proteins are measured. These results are combined with the results of a detailed ultrasound (nuchal translucency) that measures the thickness at the back of the fetus’s neck.

HOW EFFECTIVE IT IS: It has an 80 percent to 85 percent detection rate for Down syndrome, with a 4 percent to 6 percent false-positive rate.

WHAT IF …? If you have a positive screen and are not comfortable with the odds, you may opt for a diagnostic test to determine if your baby has a defect. Another option is to do an additional screen in the second trimester—but this will not give you a definitive answer, either.

full integrated screen

WHO IT’S OFFERED TO: All women (if it’s available in the area where she lives).

WHEN IT’S OFFERED: The first part is conducted at weeks 10 to 13; the second part, at weeks 14 to 20.

WHAT IT SCREENS FOR: Down syndrome.

HOW IT WORKS: Results from the first-trimester ultrasound and blood work are combined with the results from second-trimester blood work.

HOW EFFECTIVE IT IS: “It has a very high detection rate for Down syndrome—85 percent to 90 percent—with a very low false-positive rate: 1 percent to 2 percent,” O’Brien says.

WHAT IF …? If you do have a positive screen, you’ll need to decide if you’ll have amniocentesis to confirm the diagnosis (it’s too late for CVS).

second-trimester screening

WHO IT’S OFFERED TO: All women.

WHEN IT’S OFFERED: At 14 to 20 weeks.

WHAT IT SCREENS FOR: Down syndrome, trisomy 18 and neural-tube defects (NTDs) such as spina bifida.

HOW IT WORKS: Consists of a blood test that typically looks at four different proteins in the mother’s blood; often referred to as the “quad screen” or “multiple marker screening.” Unlike first-trimester screening, second-trimester tests can screen for NTDs in addition to chromosomal defects such as Down syndrome.

HOW EFFECTIVE IT IS: It has an 80 percent to 85 percent detection rate for Down syndrome, with a 7 percent false-positive rate.

WHAT IF …? If you have a positive screen for any defect, you may choose to have an amniocentesis; a level II ultrasound may also be offered.

amniocentesis

WHO IT’S OFFERED TO: Women who will be older than 35 at delivery; those who have an abnormal first- or second-trimester screening test result.

WHEN IT’S OFFERED: At 15 to 20 weeks.

WHAT IT SCREENS FOR: Chromosomal defects such as Down syndrome; developmental defects such as NTDs.

HOW IT WORKS: A small amount of amniotic fluid is extracted via a needle inserted through the abdomen and uterus.

HOW EFFECTIVE IT IS: Almost 100 percent. The risk of miscarriage from the procedure is approximately 1 in 200 to 1 in 600, depending on the skill and experience of the person performing the procedure.

WHAT IF …? If a defect is diagnosed, you’ll need to decide whether to continue the pregnancy or terminate it.