Methods used to diagnose disorders of the fetus, by entering the uterus and taking away tissue or fluid surrounding the fetus to test.
This article is pending medical review.
Written by Sophie Oppelt
Reviewed by Alizeh Ahsan and Julian Zeegers
Edited by Juliëtte Gossens
Different findings during your pregnancy check-ups can indicate the need for invasive prenatal testing. Invasive means, in this case, that the doctor obtains body tissue by introducing a tool, such as a needle, inside the body. This can be performed during a pregnancy to diagnose a disease, for example any chromosomal abnormalities of the baby. Invasive tests are usually performed when the pregnancy is indicated as “high risk”. This could be due to the mother or carrying parent being a bit older, the presence of specific family history, or when previous children were born with certain diseases. Furthermore, as soon as an abnormal result is obtained from ultrasound, blood, or NIPT (non-invasive prenatal testing) analysis, you may be offered invasive testing methods to confirm those results (1, 6). We explain what these methods involve below.
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Before Your Test
Before invasive testing is performed, prospective parents receive an extensive counselling session. In this session, the doctor explains the procedure in detail to inform you about the risks and the potential outcomes of invasive testing methods before you consent to it. There is also the opportunity to ask any questions you might have.
Depending on the blood type of the pregnant parent, something called an “anti-D” injection might be required if they are rhesus negative. This is because there is a possibility that the child is rhesus positive. If the baby’s blood were to get into the parent’s circulation during the procedure, the parent’s immune system would produce antibodies. Such antibodies could present a substantial risk for the ongoing or any future pregnancy, because the parent’s immune system could attack the baby’s red blood cells. The anti-D injection prevents this from happening. (1)
Invasive Testing Methods
There are two main invasive prenatal testing methods, chorionic villus sampling (CVS) and amniocentesis.
Chorionic Villus Sampling (CVS)
Chorionic villi are branches of the placenta, through which the nutrient exchange between parent and baby takes place. During CVS, a small sample of tissue from the placenta is taken. This tissue contains genetic information that is very similar to that of the unborn child. Tissue can either be obtained with a tube through your cervix (“transcervical”) or with a needle through your belly (“transabdominal”). The second approach is more common. For both methods, a local anesthetic (to numb the area) is applied, and the procedure is guided by ultrasound. CVS is usually performed between 11 to 14 weeks of pregnancy, for an earlier diagnosis.
The tissue sample is sequenced, which gives information about possible chromosomal abnormalities. (1-3)
Amniocentesis is performed later during pregnancy, from 15 weeks of gestation onwards. An anesthetic is not required, because this method only takes fluid from the placenta, not tissue. Similar to CVS, a needle is inserted through your belly under ultrasound guidance, removing 15 to 20 milliliters (0.5 – 0.7 fl. oz.) of amniotic fluid. The amniotic fluid contains cells from the fetus, which can be sequenced. In addition to the same results that the CVS can provide, amniocentesis allows for testing of neural tube defects. These are issues with closing of the spinal cord, such as spina bifida. (1, 4, 5)
After the Procedure
After the procedure, your doctor will likely advise you to take it easy, but won’t advise bed rest. Cramping is a common symptom for the hours after the test. Paracetamol (acetaminophen) can be taken if needed. However, if you experience bleeding, fluid leaking, or severe cramping, you should consult with your doctor. (2, 4)
Risks and possible complications
As they are invasive procedures, CVS and amniocentesis don’t come without risks. The scariest possibility is miscarriage. The risk of miscarriage is slightly lower for amniocentesis, which happens in 1 for every 200 to 400 procedures (or a 0,25%-0,5% chance). In CVS, the miscarriage rate is 1 in every 100 to 200 procedures (or a 0,5%-1% chance). There is also a very low risk of infection, induction of preterm labor, or injury to the baby. (1, 5, 6)
The results usually take one to two weeks to come back. In case of a positive test result (which means the disease that was tested for is present), prospective parents have to decide what to do: terminate the pregnancy, or use the information to prepare for the challenges of the diagnosis.
Whatever decision you decide to make, remember that you’re not alone! Thousands of parents are faced with invasive testing and disappointing test results each year. Seek support with friends and family, and perhaps with the PREhealth community.
Ultrasound Specialist Melbourne. Amniocentesis & CVS. Available from: https://www.womensultrasoundspecialists.melbourne/invasive-prenatal-testing [Accessed 5 May 2022]
NHS. Overview chorionic villus sampling. Available from: https://www.nhs.uk/conditions/chorionic-villus-sampling-cvs/ [Accessed 5 May 2022]
Monni G, Pagani G, Stagnati V, Iuculano A, Ibba RM. How to perform transabdominal chorionic villus sampling: a practical guideline. J Matern Fetal Neonatal Med. 2016;29(9):1499-505. DOI: 10.3109/14767058.2015.1051959.
NHS. Overview amniocentesis. Available from: https://www.nhs.uk/conditions/amniocentesis/ [Accessed 5 May 2022]
Evans MI, Andriole S. Chorionic villus sampling and amniocentesis in 2008. Current Opinion in Obstetrics and Gynecology. 2008;20(2):164-168. DOI: 10.1097/GCO.0b013e3282f7321f
Alfirevic Z, Navaratnam K, Mujezinovic F. Amniocentesis and chorionic villus sampling for prenatal diagnosis. Cochrane Database of Systematic Reviews. 2017;9: CD003252. DOI: 10.1002/14651858.CD003252.pub2
Please note: the information we provide to you here is for educational purposes only. If you’re experiencing any discomfort or have any complaints or questions about your health, please contact your doctor or other relevant health professional. We don’t provide medical advice.