Screening for Birth Defects
Peachtree Women’s Clinic offers screening for birth defects and genetic disorders. A birth defect is a problem with the baby that is present at birth. A birth defect may affect only one part of the body, such as the heart, spine, brain or stomach or it can affect multiple body systems. A genetic disorder is a problem with a person’s genes or chromosomes. Unlike a physical defect, genetic disorders cannot be fixed, as they are part of our DNA.
The quality of ultrasound today has helped us detect these problems before the baby is born, however, ultrasound does not guarantee a normal baby. Combining our ultrasound with a simple blood test, your doctor can help improve the detection of a problem with your baby before birth.
What is important to remember is that these tests are only screening tests – this means that they only tell us if your chances of having a baby with a birth defect is higher than what we would expect in a healthy person the same age as you. Additional testing must be performed (usually by a high-risk OB specialist) to confirm any problem. In many cases, a “positive” screen still results in a healthy, normal baby.
Below is a list of birth defects that we can screen for at Peachtree Women’s Clinic:
- Neural Tube Defects: problems that affect the baby’s brain or spine. The most common neural tube defects are spina bifida (failure of the spinal canal to close) and anencephaly (malformation of the brain).
- Abdominal Wall Defects: problems that affect the baby’s stomach wall. The most common defects are omphalocele (a hernia around where the umbilical cord inserts) or gastroschisis (a hole in the wall of the belly).
- Heart Defects: Malformation of the chambers of the heart.
- Down Syndrome: A genetic problem where an extra copy of Chromosome 21 is present. This disorder commonly results in a characteristic face, mental retardation and heart defects.
- Trisomy 18: A genetic problem where an extra copy of Chromosome 18 is present. This disorder results in severe mental retardation, multiple birth defects and is almost always fatal.
The tests must be performed at specific times during the pregnancy to ensure accurate results. Depending on your risk factors, you and your doctor can determine if genetic screening is right for you.
First Trimester Screening/Nuchal Translucency
First trimester screening is a newer screening test that helps improve the detection of birth defects when combined with our traditional screening. It allows some birth defects to be detected much earlier (before 14 weeks) that our traditional screening tests.
The first trimester test consists of two parts:
- Ultrasound Measurement of Nuchal Translucency – an ultrasound is performed of your baby between 11-14 weeks. All babies have a small pocket of fluid on the back of the neck, which is measured during this test. If the pocket is larger than expected, it can be a sign of a birth defect.
- Blood Test – The levels of two chemicals, PAPP-A and HCG, are tested.
First trimester screening can detect birth defects about 80-85% of the time.
Second Trimester Screening/”Quad Screen”/”Multiple Marker Screen”
Second trimester screening has improved over the years to include additional substances in the blood screen which has improved detection of birth defects.
The second trimester screen consists of a blood test looking at the levels of the following substances:
- Alpha fetoprotein
- Estriol
- HCG
- Inhibin-A
The quad screen can detect birth defects about 80% of the time. The detection rate of nuchal translucency is higher than quad screen alone. Therefore, the quad screen is recommended only for patients who did not undergo nuchal translucency testing.
Cell-Free Fetal DNA
Cell-Free Fetal DNA involves taking a sample of blood from the mother and isolating the baby’s DNA from the blood sample. It is recommended for women over 35, women who have had a prior pregnancy affected by trisomy or women with abnormal first trimester screening tests. While it does not replace the accuracy of amniocentesis, it provides a non-invasive method of screening for genetic problems.
Amniocentesis
Amniocentesis is a procedure in which a needle is inserted through the belly into the womb. The fluid that surrounds the baby contains the baby’s genetic information, which is sent to a lab for analysis. This analysis can look at the entire genome of the baby, or can screen for specific genetic defects that may be present in the family. Amniocentesis is usually performed between 16-18 weeks and takes 2-4 weeks for full results to come back.
