Prenatal testing for genetic or birth defects involves a number of halachic issues. With most of the available technology, the main concern is not with the procedures themselves – blood tests and ultrasounds – but with what might be done with the results.
When testing is done prior to marriage, there is a concern that it could lead to the dissolution of an otherwise appropriate union. Furthermore, misconceptions about the significance of carrier status might lead to difficulty finding a match even if there is no medical reason to fear the birth of an affected child.
When the testing is done after marriage, there is concern that it might inhibit the couple from having children. If the testing is done after conception there is the concern that it might lead to an abortion.
On the other hand, if the prenatal test will lead to an intervention that would be beneficial to the health of the fetus, then there is reason to permit it.
Testing for genetic diseases comprises two forms of testing: testing for hereditary disease and testing for abnormal chromosome number.
Ideally, couples will have been screened for hereditary diseases prior to marriage. If a couple has not been tested prior to marriage, they can be tested pre-conception. If both members of the couple are found to be carriers for a significant genetic disease, in-vitro fertilization with pre-implantation genetic diagnosis (IVF-PGD) may be permitted. Each couple considering this procedure must ask an individual halachic question. Where there is a known family history of a genetic defect, it is likely that IVF will be permitted to allow pre-implantation genetic diagnosis. It is halachically much easier to allow implantation of unaffected fetuses than to allow abortion.
Once conception has taken place, then the only remaining intervention is abortion. Abortion is not easily permitted for a malformed but viable fetus. However, as halacha is case law, an individual question should always be asked.
Testing for abnormal chromosome number is performed during pregnancy.
Screening Tests During Pregnancy
Currently, screening for chromosomal or developmental abnormalities includes first-trimester risk assessment at 11 to 14 weeks (this may include ultrasound nuchal cord thickness assessment) and maternal blood test screening at 15 to 20 weeks.
With the AFP, quad, and penta screening tests, an unusually high or low level of specific indicators in a woman's blood indicates a higher probability of certain fetal defects. Where alpha fetoprotein (AFP) is high, there is a greater risk that the fetus has a neural tube defect such as anencephaly (lack of a skull) or spina bifida (hole in the spinal cord). Where AFP is low, the chances are greater that the fetus has Down Syndrome (Trisomy 21, an extra copy of the 21st chromosome). When these measurements are combined with those for 2-4 other proteins (triple, quad, or penta test), the ability to statistically predict Down Syndrome is even better. The test may be useful in detecting other chromosomal abnormalities as well.
Before this test is performed, a couple should be aware of its meaning and implications. It is important to remember that it is only a screening test. While an abnormal reading indicates a greater chance that the fetus is affected, it is definitely not a diagnosis. Most women with positive test results will have completely healthy babies.
In practice, if the results are negative, one can relax and be reasonably confident that the fetus is not affected. If the results are positive, chances are still good that the fetus is not affected. But the woman's physician will probably suggest further testing to determine whether there is a problem.
Most rabbis would permit AFP screening to screen for anencephaly or spina bifida. While a specific question must be asked, it is quite likely that pregnancy interruption would be permitted for anencephaly as the fetus has no life expectancy. Allowing abortion for spina bifida would be a much more difficult question. However, a prenatal diagnosis of spina bifida allows a woman to choose a method of delivery and a hospital that will enable optimal treatment for the baby. There is room to permit the test – as well as amniocentesis if needed for a definite diagnosis – for this reason.
Using the triple, quad, or penta test to screen for Down Syndrome is a matter of halachic debate. A definite diagnosis will require a more invasive test (amniocentesis or CVS, see below), which is more halachically problematic. Permitting abortion following such a diagnosis would be halachically very difficult. Therefore, each couple should discuss the implications of such screening with each other and with their rabbi before deciding whether to be tested.
Currently, it is clinically possible to isolate fetal DNA from maternal blood during pregnancy. While this could be considered a diagnostic procedure, at present it is not considered reliable enough to be the sole form of diagnosis and thus it too needs follow up by an invasive procedure.
Amniocentesis and Chorionic Villi Sampling
There is halachic debate regarding the permissibility of invasive prenatal tests (amniocentesis and chorionic villi sampling). In cases where the fetus is clearly not viable, (such as Trisomy 18), many authorities would permit abortion and thus amniocentesis would be allowed. But for other defects such as Down syndrome, where abortion is generally not permitted, rabbinic authorities differ. Some authorities maintain that, since abortion is not an option, one should not increase the risk of miscarriage with an invasive test. Other authorities consider the test worthwhile because in most cases the fetus is not affected and the parents can then be relaxed about this issue. Even if the fetus is affected, the family may be more able to cope if they are prepared in advance. A couple considering these tests should discuss them with their rabbi before they are performed.
Amniocentesis is performed via the abdomen and is unlikely to cause vaginal bleeding; therefore, it does not render a woman niddah.
Chorionic villi sampling (CVS) used to be done as early as 6 weeks of gestation. This was helpful for religious couples, as it was just possible to get results within 40 days after mikvah immersion, when it is easier to permit abortion. However, due to the risk of limb defects, this test is no longer performed quite so early in pregnancy and this advantage is lost. CVS continues to have the advantage that it can be performed early enough that a woman can still hide her pregnancy. This needs to be balanced against the slightly higher risk of miscarriage than that for amniocentesis. The couple should ask for the statistics for the center where the procedure is done prior to consulting with the rabbi.
There is debate as to whether this procedure makes a woman niddah. This question should also be asked prior to its performance.
Ultrasound for prenatal screening
There is generally little halachic objection to the use of ultrasound examinations during pregnancy. The procedure is safe and non-invasive.
A second trimester ultrasound is often done to look for structural abnormalities in the fetus. The ultrasound itself presents no halachic issues. Knowing in advance about abnormalities can, at times, allow for delivery in the appropriate care setting and increase the infant's chance of survival. That goal is halachically encouraged. Finding abnormalities to allow for abortion is more difficult although in certain extreme cases it might be permitted. Case specific questions need to be asked.
Ultrasound may be done by placing an external transducer (which emits sound waves) over the abdomen. This certainly does not render a woman niddah.
Sometimes, a transducer may be inserted into the vagina. It does not enter the uterus and is unlikely to cause bleeding, so this test generally does not render a women niddah. If blood is noted on the transducer, the woman should ask her physician what is the most likely source and then consult a rabbi.
Nuchal Cord Thickness
The halachic issues raised by measuring nuchal cord thickness to screen for Down syndrome are similar to those for other ultrasound examinations. The couple should discuss the accuracy and implications of this test with their physician before it is performed. They can then consult with their rabbi to decide what to do with the results. If the rabbi will not permit a follow up test, measuring nuchal cord thickness alone is of questionable value.