Prenatal Testing | Fit Pregnancy

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.


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.


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.


Who it's offered to: All women.

When it's offered: At about 20 weeks (also offered as part of the first-trimester screening).

What it screens for: A wide variety of problems. “An anatomical survey of the entire fetus is typically conducted,” explains midwife Barbara McFarlin.

How it works: Using a transducer placed over the abdomen, sound waves create pictures of the fetus.

How effective it is: McFarlin says it detects approximately 50 percent of heart defects; O’Brien says it’s excellent at detecting NTDs. However, O’Brien adds: “Fifty percent of babies born with Down syndrome had normal ultrasound results.”

What if ...? If ultrasound does detect a potential problem, you’ll need to decide if you want an amnio to determine whether it could be part of a chromosomal or genetic syndrome.


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