Many mothers seek out prenatal paternity testing in order to identify the father of their baby while they are still pregnant. The 2 most widely used invasive methods for this are Amniocentesis and Chorionic Villus Sampling (CVS). Both are used for detecting paternity, but they also help detect free chromosomal and genetic abnormalities in the fetus. While both procedures serve a similar diagnostic purpose, they differ in terms of timing, technique, risks, and applications. This guide provides a detailed comparison of amniocentesis and CVS, including their roles in paternity testing.
What Is Amniocentesis?
Amniocentesis is an invasive procedure generally performed between the 15th and 20th weeks of pregnancy. It involves inserting a fine needle through the abdominal wall into the uterus under ultrasound guidance. A small sample of amniotic fluid is withdrawn, which contains fetal cells and substances used for genetic and biochemical testing.
Common indications for amniocentesis include:
- Detection of chromosomal abnormalities like Down syndrome (Trisomy 21)
- Diagnosis of neural tube defects such as spina bifida
- Screening for inherited genetic conditions such as cystic fibrosis
- Fetal lung maturity assessment later in pregnancy
- Determining fetal infections or Rh incompatibility
Use in Paternity Testing
Amniocentesis can also be used to establish paternity before birth by analyzing fetal DNA found in the amniotic fluid. DNA is extracted and compared with samples from the alleged father. This method offers accuracy comparable to postnatal paternity testing.
What Is Chorionic Villus Sampling (CVS)?
CVS is another form of invasive prenatal testing performed earlier than amniocentesis, typically between the 10th and 13th weeks of pregnancy. The procedure involves obtaining a small sample of placental tissue (chorionic villi), which shares the fetus’s genetic makeup.
There are two approaches:
- Transcervical: A catheter is guided through the cervix to collect the sample.
- Transabdominal: A needle is inserted through the abdomen, similar to amniocentesis.
CVS is used primarily to detect chromosomal abnormalities and genetic disorders, as well as determining paternity. However, unlike amniocentesis, it cannot detect neural tube defects due to the absence of amniotic fluid sampling.
How Soon Can You Do Amniocentesis or CVS?
One of the main differences between CVS and amniocentesis is the timing when you are able to undergo the procedure
- CVS: 10–13 weeks gestation (first trimester)
- Amniocentesis: 15–20 weeks gestation (second trimester)
The earlier availability of CVS allows for faster decision-making if an abnormality is detected, which can be vital for some parents.
How Accurate Is Amniocentesis and CVS Testing?
Both tests offer high diagnostic accuracy:
- Amniocentesis: Approximately 99.4%–100% accuracy for chromosomal abnormalities
- CVS: Approximately 98%–99% accuracy
While CVS allows earlier detection, amniocentesis has a broader diagnostic scope, including testing for neural tube defects and certain fetal infections.
Risks and Complications
Amniocentesis Risks:
- Miscarriage risk is about 0.1% to 0.3% after 15 weeks
- Minor discomfort, cramping, or amniotic fluid leakage
- Very rare chance of injury to the fetus or infection
CVS Risks:
- Miscarriage risk ranges from 0.5% to 1%
- Increased risk if performed before 10 weeks (limb abnormalities)
- Maternal cell contamination can affect test accuracy
When performed by experienced professionals, both procedures are considered relatively safe, with CVS carrying a slightly higher risk. However, both are still higher risk than Non-invasive Prenatal Paternal (NiPP) testing.
Legal and Ethical Considerations
Both tests raise important ethical and legal considerations, particularly concerning selective termination and the psychological impact of discovering a fetal abnormality. Some jurisdictions may also have regulations regarding how and when these tests can be performed, especially in the context of sex-selective or paternity-related testing.
Pre- and post-test genetic counseling is highly recommended to support decision-making and to ensure that parents understand the implications of the test results.
Conclusion
Amniocentesis and Chorionic Villus Sampling are valuable tools in prenatal diagnosis, each with its own advantages and limitations. CVS offers earlier detection, which can be crucial for early decision-making, while amniocentesis provides a broader range of diagnostic information, including the detection of neural tube defects. The choice between the two should be made in consultation with healthcare providers, considering the specific needs and circumstances of the pregnancy.
