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Diagnostic Tests

Diagnostic tests in pregnancy are used to definitively confirm or rule out a chromosomal condition. These tests are invasive, which means they carry a small risk of miscarriage.  Most miscarriages will occur in the first 72 hours following a procedure, but there is still a risk of miscarriage for up to two weeks after the diagnostic test, but it is much less likely to happen.

In multiple pregnancies, diagnostic tests can be used to test each baby.  However, the risk of miscarriage is higher in multiple pregnancies so please ensure you discuss this with your healthcare provider.
 

Chorionic Villus Sampling

CVS is usually performed when a test is required in early pregnancy, commonly from around 11-14 weeks.A thin needle is passed either through the abdomen or the vagina to take a small sample from the cells of the placenta. The placenta and the baby develop from the same cells, so this can give important information about the baby's chromosomes.

The samples will be sent to the laboratory for analysis.  Initial results are usually available within three days, with a full result following at around two weeks. CVS Test results are considered to be 99% effective. Occasionally it will not be possible to perform the full testing on a placental sample.  If this happens, it it likely you will be offered an amniocentisis.

CVS carries around a 1% risk of miscarriage.  The reason for this is not known.  Most miscarriages will occur in the first 72 hours following a procedure, but statstically the risk remains higher for up to 14 days.

More information on CVS can be found on the NHS website here.

Amniocentesis

Amniocentesis is a true reflection of the baby’s DNA rather than DNA from the placenta, so some women prefer to wait and have an amniocentesis rather than a CVS.

Amniocentesis is performed from 15 weeks of pregnancy onwards. (Before this time there is not enough amniotic fluid to safely take a sample). Using ultrasound scan for guidance, a needle is inserted through the woman's abdomen to obtain a small sample of amniotic fluid, which contains cells from the baby. 

The samples will be sent to the laboratory for analysis.  Initial results are usually available within three days, with a full result following at around two weeks. Amniocentesis results are considered to be 98-99% accurate. 

1 in 150 woman who have an amniocentesis will experience a miscarriage thereafter.  The reason for this is not known.  Most miscarriages will occur in the first 72 hours following a procedure, but statstically the risk remains higher for up to 14 days. 

More information on Amniocentesis can be found on the NHS website here.

Cordocentesis

This test is carried out after the 18th week of pregnancy, usually if a CVS and/or amniocentesis have been inconclusive. A needle is inserted into the mother's abdomen and a sample of the baby's blood is taken from the umbilical cord.

Results take between 4-7 days. 

The risk of miscarriage from a cordocentesis is between 1-2%.  It also carries some additional risks to the health of both mother and baby. It is important to discuss these risks with your healthcare provider. 

 

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