Diagnostic Procedures
Prenatal Diagnosis
Most babies are born healthy. However, birth defects happen in about 3 out of every 100 births. Some birth defects can be diagnosed before a baby is born.
Prenatal diagnostic procedures are medical tests done during pregnancy to find certain birth defects. They include amniocentesis and chorionic villus sampling (CVS). There is a very low risk of miscarriage or loss of the baby from either of these procedures.
Chromosome conditions are the most common birth defects that are found by a diagnostic procedure. These procedures may also be done when genetic carrier screening or the family history shows a risk for an inherited genetic disease, such as cystic fibrosis and sickle cell disease.
Deciding whether to have diagnostic testing
Diagnostic testing gives you the most complete information about birth defects in the developing baby. It is always your choice to have a diagnostic test. You can choose to start with this type of testing or ask for diagnostic testing if a blood test or ultrasound shows a high risk for birth defects.
The decision to have a diagnostic test is personal. It can help to talk with your doctor, nurse practitioner, nurse midwife, or genetic counselor.
Keep in mind:
- Diagnostic testing can give you information about the baby's health before birth.
- Knowing about a chromosome condition (or other birth defects) during pregnancy may help you make decisions about medical care.
- Diagnostic procedures have a small risk of miscarriage or loss of the pregnancy.
- Diagnostic testing does not detect all birth defects or genetic conditions.
Summary of Prenatal Diagnostic Procedures
|
|
Amniocentesis |
CVS |
|
Procedure |
Amniotic fluid is taken by a thin needle through the abdomen, without touching the baby |
Chorionic villi are taken by a thin plastic tube through the vagina (transcervical)
|
|
Timing |
15 to 22+ weeks. |
10 to 13+ weeks. |
|
Accuracy of Chromosomal Analysis
|
Greater than 99% accuracy |
Greater than 99% accuracy |
|
Neural Tube Defects (NTDs)
|
Detects 9 out of 10 babies with NTDs (using AFP from the fluid)
Ultrasound done at 18 to 22 weeks detects most NTDs |
Does not detect NTDs.
Blood test done between 15 and 21 weeks detects 8 out of 10 babies with NTDs
Ultrasound done at 18 to 22 weeks detects most NTDs
|
|
Results
|
About 2 weeks |
About 2 weeks |
|
Miscarriage Due To Procedure
|
About 1 in 1000 |
About 1 in 1000 |
|
Vaginal Bleeding
|
Rare |
Vaginal spotting sometimes happens |
|
Cramping
|
Occasional, usually mild |
Occasional, usually mild |
|
Infection, Fluid Leakage |
Uncommon
|
Uncommon |
|
Injury To Fetus
|
Extremely rare |
Extremely rare |
|
Frequency of Repeat Procedure
|
Less than 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: October 2022
Reviewed by: Kimberly Barr, LCGC, Kaiser Permanente NCAL Regional Genetics