Prenatal Screening for Birth Defects
Posted on Tuesday, November 10th, 2015 at 4:05 pm
A pregnant woman can undergo fetal screening for certain birth defects during her pregnancy. Birth defects may be caused by problems with genes, chromosomes, or exposure to certain agents. However, 70% of birth defects have no known cause.
Prenatal screening tests can show whether you are at high risk or low risk of having a baby with a particular disorder.
If the screening test shows that you are high risk for a birth defect, a diagnostic test will have to be done to determine if your baby actually has the disorder.
Here are some screening tests which can help determine your baby’s risk of having a birth defect.
Prenatal Screening Tests
| Screening Test | Test Type | What Does It Screen For? | Detection Rate |
|---|---|---|---|
| Combined first trimester screening (11-13 weeks gestational age) | Blood test plus an ultrasound exam | Trisomy 21 Trisomy 13 Trisomy 18 |
82–87% |
| Second trimester single screen for neural tube defects (14-16 wga) | Blood test | Neural tube defects | 85% |
| Second trimester quad screen (15-20 wga) | Blood test | Trisomy 21 Trisomy 18 Neural tube defects |
81% |
| Integrated screening | Blood and an ultrasound exam in the first trimester, followed by quad screen in the second trimester | Trisomy 21 Trisomy 18 Neural tube defects |
94–96% |
| Panorama Screen also known as cell free fetal DNA test (>10 wga) | Blood test that looks at fetal DNA in mother’s blood | Trisomy 21 Trisomy 13 Trisomy 18 Neural tube defects Sex chromosome abnormalities Microdeletions |
>99% |
Glossary
- Trisomy:
- a condition in which there is an extra chromosome.
- Monosomy:
- a condition in which there is a missing chromosome.
- Trisomy 13:
- Patau syndrome is a genetic disorder characterized by heart defects and other developmental problems. Most affected infants die within the first year of life.
- Trisomy 18:
- Edwards Syndrome is a genetic disorder that causes serious mental and developmental problems. Most affected infants die within the first year of life.
- Trisomy 21:
- Down Syndrome is a genetic disorder in which abnormal features of the face and body, medical problems such as heart defects, and intellectual disability occur.
- Monosomy X:
- Turner Syndrome is a condition affecting females in which there is a missing or damaged X chromosome. It causes a webbed neck, short height, and heart problems.
- Neural Tube Defect:
- Birth defects of the brain, spine, or spinal cord. The most common neural tube defects are spina bifida and anencephaly. In spina bifida, the fetal spinal column doesn’t close completely. In anencephaly, most of the brain and skull do not develop.
Information adapted from ACOG Patient Information FAQ 165