Diagnostic tests may be performed where there is reason to suspect that the fetus may have a genetic anomaly, such as in the case of advanced maternal age, family medical history, or abnormal screening tests.
Prior to proceeding with these tests, it is important to ask the medical team why the test is recommended, what information may be learned, what may be gained from having this information, and what risks the test entails. These considerations should be discussed with one’s health care provider in order to make a shared decision about the procedure.
We follow the view that this information, and the relative necessity of performing an invasive procedure, should be discussed with an experienced halachic authority prior to undergoing these tests.
Chorionic Villus Sampling (CVS) typically offered during weeks 10-13 of pregnancy, is a test in which a small sample of placental tissue is obtained and analyzed. Since the placenta and the fetus almost always share the same genetic material, this testing can confirm or diagnose a genetic anomaly. However, it will not test for neural tube defects.
CVS holds some advantage over amniocentesis, since it is performed earlier in pregnancy, which may open up more options for follow-up. However, not all women are candidates for CVS, and the results are not always 100% conclusive.
There are various methods of performing CVS. In the transabdominal method, the provider inserts a needle through the abdomen and into the uterus to withdraw the sample. A transabdominal procedure does not make a woman niddah.
The transvaginal method involves directing an ultrasound-guided catheter (small tube) through the vagina and into the cervix, and then using a small syringe at the far end of the catheter to remove some placental tissue.
With transvaginal CVS, a woman should ask her doctor about the diameter of any instruments inserted into the cervix. The catheter size is commonly 17mm (5.3Fr) or 20mm (5.7Fr). We follow the halachic position that instruments narrower than 19mm in diameter do not render a woman niddah (learn more here). Therefore, insertion of a 17mm catheter would not make a woman niddah, whereas a 20mm catheter would.
A woman may have staining after CVS. This is generally due to trauma to the placenta, cervix or the uterus during the procedure. We follow the position that this bleeding is dam makkah and does not make a woman niddah. Nevertheless, it is recommended to take precautions, such as wearing colored underwear or disposable pantyliners, to avoid any questions.
Depending on the route and timing of the CVS procedure, it may be associated with slightly increased risks to the pregnancy, such as pregnancy loss or limb-deformity.
Amniocentesis is a diagnostic test in which a small sample of amniotic fluid is obtained in order to test for chromosomal defects, neural tube defects, or other potential genetic anomalies. This test is typically offered during weeks 15-20 of pregnancy. A long, thin needle, guided by an ultrasound, is inserted through the abdomen and into the amniotic sac to withdraw a sample of the amniotic fluid. The fluid contains cells from the fetus that can be tested for genetic information.
Because the test is performed through the abdomen, it is unlikely to cause vaginal bleeding, and does not make a woman niddah.
There is a slight increase in the risk of miscarriage following an amniocentesis, although the exact percentage of risk is dependent on various factors including week of pregnancy, practitioner experience, positioning of the fetus, and more. These risks should also be discussed with one’s medical practitioner in advance.
