Diagnostic tests involve analyzing cells from the foetus. As they incur a risk of a miscarriage, they should only be done when it has already been determined that there is a high risk of chromosomal abnormality in the pregnancy.
A pregnancy is at high risk if a screening test has indicated so, or if the mother has previously had a pregnancy affected by a chromosomal disorder.
Before taking a diagnostic test, the mother should think about what the result will mean to her. If she is going to keep the baby despite the test results, then the test may be an unnecessary risk to the pregnancy.
After taking a diagnostic test, the mother should rest for the next day. There may be slight cramping. If the vagina begins to bleed or leak fluid, the hospital should be contacted.
There are two types of tests: Amniocentesis and Chorionic Villus Sampling.
In the amniocentesis test, a needle is inserted through the mother's abdomen into the area surrounding the fetus. The needle extracts a sample of amniotic fluid for analysis. This process takes 5-10 minutes. It may take over two weeks to get the final results of the test, however a preliminary one is sometimes available after two days.
There is a 0.5 - 1 percent chance of a miscarriage happening within three weeks of the test.
Chorionic Villous Sampling (CVS)
In the CVS a sample of the placenta is analyzed. The procedure is similar to amniocentesis: a needle is inserted through the mother's abdomen into the placenta, and a small sample is extracted. This usually takes about 5-10 minutes and is slightly more uncomfortable than amniocentesis. It may take up to two weeks to get a final result, but again, a preliminary one is usually available within two days.
There is a 1-2 percent chance of miscarriage after having a CVS test.
As stated above, both tests introduce a small chance of a miscarriage occurring.
After either test, the mother should rest for the next day. If the vagina leaks fluid or bleeds following the test, contact the hospital or your health care provider immediately.
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