Diagnostic Procedures
Prenatal Diagnosis
Most babies are born healthy. However, every pregnant woman has a small chance of having a baby with a birth defect. Birth defects generally occur in about 3 out of every 100 births. Prenatal diagnostic procedures are medical tests which can be performed during pregnancy to detect certain birth defects.
There are many different kinds of birth defects, but only a few can be diagnosed prior to the baby's birth. Chromosome abnormalities and neural tube defects are the most common birth defects that we look for with routine prenatal diagnosis procedures. Occasionally, prenatal diagnosis procedures are done to detect certain genetic diseases, such as cystic fibrosis and sickle cell disease. This specialized testing is offered when a pregnancy is known to be at-risk for a genetic disease. Sometimes, the risk is based on genetic carrier testing in the parents, other times it may be related to a family history of a genetic disease.
Prenatal diagnostic procedures include amniocentesis and chorionic villus sampling (CVS). Amniocentesis and chorionic villus sampling (CVS) can detect specific birth defects, such as chromosome abnormalities. Both procedures have a small risk of miscarriage or loss of the baby (about 1 in 300 or less).
Deciding whether to have a prenatal diagnostic procedure
Some women decide that even though there is a small risk for miscarriage, they would like to have a prenatal diagnosis procedure to find out whether the baby has a chromosome abnormality. Other women only choose a diagnostic procedure after having a positive prenatal screening test. It is your choice whether or not to have a prenatal diagnostic procedure.
The decision to have a prenatal diagnostic procedure is a very personal one. You may want to discuss the risks, benefits and limitations of such testing with your doctor, nurse practitioner, nurse midwife, or a genetic counselor.
Keep in mind:
- Prenatal diagnostic procedures can provide you with some information about the baby's health before birth, such as whether the baby has a chromosome abnormality.
- Chromosome abnormalities are not curable.
- Prenatal diagnostic procedures have a small risk for miscarriage or loss of the pregnancy.
- There are no prenatal diagnostic procedures that can detect all birth defects before birth.
Summary of Prenatal Diagnostic Procedures
| Amniocentesis | CVS |
Procedure | Amniotic fluid is removed by needle | Chorionic villi are removed by catheter (transcervical) or by needle (transabdominal), depending on location of placenta
|
Timing | 15 - 20+ weeks. Early amnio is done between 14th and 15th week.
| 10 - 13+ weeks. |
Accuracy of Chromosomal Analysis
| Greater than 99% accuracy | Greater than 99% accuracy |
Neural Tube Defects (NTDs)
| AFP measured in amniotic fluid, with NTD detection rate of 90 - 95%
Ultrasound done about 18-20 weeks can detect most NTDs | Does not detect NTDs.
Maternal AFP blood test offered between 15 and 20 weeks, with NTD detection rate of 80 - 85%
Ultrasound done about 18-20 weeks can detect most NTDs
|
Results
| About 2 weeks | About 2 weeks |
Miscarriage Due To Procedure
| < 1 in 300. (Early amnio: < 1 in 100) | < 1 in 300 |
Vaginal Bleeding
| Rare | Spotting may occur after transcervical CVS |
Cramping
| Occasional, usually mild | Occasional, usually mild |
Infection, Fluid Leakage | Uncommon
| Uncommon |
Injury To Fetus
| Extremely rare | Extremely rare |
Frequency of Repeat Procedure
| <1 in 300 (0.3%) | 3-5% |
Restriction of Activities | Limit physical activity for 24 hours after procedure (no sexual intercourse, strenuous exercise) | Limit physical activity for 24 hours after procedure (no sexual intercourse, strenuous exercise) |
Last reviewed: January 10, 2013
Reviewed by: Kaiser Permanente Genetics