Mount Auburn Hospital - Great Expectations

TYPES OF TESTS Prenatal genetic screening and diagnostic tests can provide valuable information about your baby’s health. There are 2 main categories of tests: • Screening test – Measures a baby’s risk of developing a disease or medical condition. • Diagnostic test – Determines if a baby actually has a disease or medical condition. Prenatal genetic tests can detect 3 categories of genetic issues: chromosomal abnormalities , carrier disorders , and neural tube defects . You’ll find each of these categories discussed over the next few sections.

CHROMOSOMAL ABNORMALITIES Chromosomal abnormalities can cause specific birth defects. Every person has 23 pairs of chromosomes in their body, 1 from each parent. Sometimes an extra chromosome will appear on a pair (3 instead of 2) or 1 chromosome of a pair is lost (1 instead of 2). Either of these issues can cause a birth defect. The most common condition caused by a problem with the baby’s chromosomes is Down syndrome, which occurs in approximately 1 in 800 babies.

SCREENINGS FOR CHROMOSOMAL ABNORMALITIES

Screening tests for chromosomal abnormalities are done in the first and second trimesters. Blood samples are taken from the parent to look at certain hormones and proteins (markers). The results of these tests can be used separately or together to see if the baby is at risk for a chromosomal abnormality.

CELL-FREE DNA TESTING (NONINVASIVE PRENATAL SCREENING, OR NIPS)

Can be done as early as 10 weeks. This blood test measures fetal DNA levels from certain chromosomes in your blood.

Combined results from an ultrasound and a special blood test. The ultrasound checks how much fluid is under the skin fold along the back of the baby’s neck. This is called nuchal translucency screening. The blood test looks at 2 specific proteins in your blood. A special blood test called a quad screen analyzes 4 substances produced by the baby and the placenta. A formula is used to determine the probability of a chromosomal abnormality. If the first trimester screening test was done, blood can be drawn between 15 and 18 weeks to measure maternal serum alpha-fetoprotein to screen for neural tube defects.

FIRST TRIMESTER SCREENING (10-13 WEEKS)

SECOND TRIMESTER SCREENING (15-22 WEEKS)

If any of these tests show an increased risk of abnormalities, you may be offered additional diagnostic testing and genetic counseling.

ALPHA FETOPROTEIN

Sequential Screening Test – Combines measurements from the first and second trimester blood tests and an ultrasound exam to check for neural tube defects and genetic abnormalities.

Integrated Test – Uses results from the first and second trimester screenings to provide a single estimate of the risk of neural tube defects and genetic abnormalities.

Your Guide to A Healthy Pregnancy

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