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Chorionic Villus Sampling and amniocentesis may offer remarkably accurate prenatal diagnoses, but could these tests be missing part of the picture? New research suggests that they do, and that abnormal cells may be repaired down the line.

Older pregnant women and those who are at an increased risk of having children with genetic abnormalities — due to a family history, for instance — are frequently advised to undergo prenatal diagnostic tests. Deciding whether or not to undergo these tests is an extremely personal process. Some parents would like to be aware of fetal abnormalities in advance simply in order to prepare, while others may decide to terminate the pregnancy in the face of abnormal results.

For parents in both groups, undergoing the tests can be a nerve-wrecking experience. How reliable are the results of these tests, though? New research offers some fascinating insights. 

What Do Chorionic Villus Sampling And Amniocentesis Do?

Chorionic Villus Sampling, or CVS, is a prenatal diagnostic test that is carried out between 10 and 13 weeks of pregnancy. The test involves taking cells from the chorionic villi on the baby's placenta, allowing medical professionals to determine fetal abnormalities with great accuracy. Like the more well-known amniocentesis, CVS can pinpoint the presence of nearly all chromosomal abnormalities (though not their severity), as well as hundreds of different genetic disorders. Neural tube defects such as spina bifida can't be detected using CVS, however. 

Amniocentesis is a procedure in which a needle is guided through the pregnant woman's abdomen in order to extract amniotic fluid. Again, this fluid can be used to accurately diagnose a great many genetic disorders and chromosomal abnormalities, as well as neural tube defects. It is even used to determine lung maturity and anemia during the third trimester of pregnancy in some cases, however, amniocentesis is generally carried out between 13 and 20 weeks into a pregnancy. 

Both CVS and amniocentesis do carry a small risk of miscarriage.

Amniocentesis is, when carried out during the second trimester of pregnancy, estimated to come with a 0.6 percent risk of miscarriage, as well as having the potential to accidentally inject the baby. Chorionic Villus Sampling has an even lower risk of miscarriage. The main result of an abnormal test result is, however, that parents face the difficult task of deciding whether or not to go ahead with their pregnancy. 

Fetal Cell Repair Is Possible

New research, published in the journal Nature Communications shows, surprisingly enough, that although the results amniocentesis and CVS offer are accurate at the time the tests are performed, the greater picture may be more complex. Professor Zernicka-Goetz and her colleagues from the Department of Physiology, Development and Neuroscience at the University of Cambridge in the United Kingdom wanted to find out what happens to those abnormal cells detected during these prenatal tests. 

In order to get their results, the team mixed early mouse embryos containing normal cells with abnormal cells. The outcome was amazing. Even in mouse embryos that contained 50 percent abnormal cells, normal cells gradually started taking those abnormal cells over, eventually leading to a complete correction. Despite that, the abnormal cells remained detectable within the placenta. 

The lead author of the study had an abnormal CVS test result herself, that showed that 25 percent of the cells in her baby's placenta diverged from the norm. Her child was born healthy, but the test result inspired her to conduct this study. She said: 

"Many expectant mothers have to make a difficult choice about their pregnancy, based on a test whose results we don't fully understand. What does it mean if a quarter of the cells from the placenta carry a genetic abnormality? How likely is it that the child will have cells with this abnormality, too? "

Zernicka-Goetz commented that the findings of her study showed an embryo has "an amazing ability to correct itself". Should the mouse findings be applicable to humans as well, something to be determined during further research, it would explain why abnormal prenatal test results do not necessarily mean a baby will be born with a birth defect. This could have a great impact on future opinions of the weight of these prenatal tests, most remarkably potentially being able to prevent terminations of fetuses that would otherwise have self-corrected abnormal cells.

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