Prenatal Testing

Prenatal Testing and Screening

Several tests are available to a woman during her pregnancy. They will be offered to her by her health care provider for various reasons. Below are some of the who, why, when, how, and risks associated with some of the more commonly performed prenatal tests.

AFP (Alfa-fetoprotein) Screening

Who
The mom-to-be
Why
To assist in the detection of neural-tube defects (spina bifida), severe kidney or liver disease, and Down Syndrome
When
Between the 16th and 20th week of pregnancy
How
Blood test
Risks
None, except possible bruising or soreness at the blood withdrawal (needle) site.

There is a high incidence of false positive test results; this means that many tests are reported as abnormal, but further testing proves the baby to be normal. Women with positive tests are offered further testing such as: Triple Screen or Quad Screen (blood tests), Ultrasound examination and amniocentesis.

Amniocentesis

Who
Moms-to-be who:
1. Are over 35 years of age
2. Already have a child with a birth defect
3. Have a family history of a genetic disorder
Why
To test for chromosomal abnormalities and genetic birth defects
When
Between the 15th and 18th week of pregnancy
How
A needle is inserted through the abdomen and guided by ultrasound into the amniotic fluid (the fluid that surrounds the baby) - a small sample of the fluid is removed and tested.
Risks
Miscarriage is the primary risk related to amniocentesis. The risk of miscarriage ranges from 1 in 400 to 1 in 200. In facilities where amniocentesis is performed regularly, the rates are closer to 1 in 400 1. Some cramping or spotting can be experienced after the procedure.

CVS (Chorionic Villus Sampling)

Who
Moms-to-be who:
1. Are over 35 years of age
2. Already have a child with a birth defect
3. Have a family history of genetic a disorder
Why
Chorionic villus sampling detects chromosome abnormalities (i.e. Down syndrome) and genetic disorders (i.e. cystic fibrosis.). This test is different from amniocentesis in that it does not allow for testing for neural tube defects. 2
When
Between 10th and 12th week of pregnancy
How: Using ultrasound for guidance, a thin catheter is inserted through the cervix to the placenta- a small sample of chorionic villi cells are gently suctioned into the catheter (this is the most common method).
Risks
Because CVS is an invasive diagnostic test, it poses potential risks. Miscarriage is the primary risk related to CVS, occurring 1 out of every 100 procedures. 3

Prenatal Ultrasound

Who
Almost all pregnant women in the United States have at least one
ultrasound exam during their pregnancy
Why
Some of the more common reasons for performing ultrasound exams
include (but are not limited to) the following:
Confirm viable pregnancy, confirm heartbeat, measure size to determine
gestational age, confirm multiples in pregnancy, and verify dates and growth
When
May be performed at any time during a pregnancy
How
A clear gel is placed on the abdomen. It serves as a conductor for sound
waves, allowing them to travel through a transducer, into the uterus and
then back to the transducer to create a picture of the baby.
Risks
After 30 years of ultrasound testing, there are no known risks. Ultrasound
is believed to be safe for mother and baby.

Footnotes

  1. American Pregnancy Assn., Compiled using information from the following sources: Williams Obstetrics Twenty-Second Ed. Cunningham, F. Gary, et al, Ch. 13. Mayo Clinic Complete Book of Pregnancy & Babys First Year. Johnson, Robert V., M.D., et al, Ch. 6.
  2. Ibid.
  3. Ibid.