Invasive procedures
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Chorion villus sampling (CVS) at 11-13 weeks
CVS involves the examination of chorionic villi (placental tissue). Both the baby and placenta (afterbirth) originate from the same cell and so the chromosomes present in the cells of the placenta are the same as those of the baby.
CVS procedure leaflet
How is CVS done?
Local anaesthetic is given. A needle is then passed through the mother’s abdomen and a sample of villi is taken. The needle is carefully watched with an ultrasound scan to ensure it does not injure the fetus. The procedure lasts 2-3 minutes and afterwards we check that the fetal heart beat is normal.
What should I expect after the CVS?
For the first couple of days you may experience some abdominal discomfort, period-like pain or a little bleeding. These are relatively common and in the vast majority of cases the pregnancy continues without any problems. You may find it helpful to take simple painkillers like paracetamol. If there is a lot of pain or bleeding or if you develop a high temperature please seek medical advice.
When can I expect to get the results?
A preliminary result is usually available within 3 days and a final result within 2-3 weeks. As soon as we get the results, we will call you to let you know.
Will the procedure need to be repeated?
In approximately 1% of cases the invasive test will need to be repeated. This is because the cells have failed to grow in the laboratory or the results are inconclusive.
What are the risks associated with the test?
The risk of miscarriage due to CVS is about 1% and this is the same as the risk from amniocentesis at 16 weeks. If you were to miscarry due to the test, this would happen within the next week.
Some studies have shown that when CVS is performed before 10 weeks, there is a small risk of abnormalities in the babies fingers and/or toes. To avoid this risk, we never perform CVS before 11 weeks.
Amniocentesis after 14 weeks
Amniocentesis involves passing a thin needle into the uterus in order to remove fluid from around the fetus.
This test gives the same information as CVS but it is carried out from 14 weeks onwards and the results are known in 2 to 3 weeks.
The risk of miscarriage is about 1% the same as for CVS.
Although amniocentesis can also be performed at 11 to 13 weeks, studies have shown that CVS is safer at this stage.
Cordocentesis after 20 weeks
Cordocentesis involves passing a thin needle into the uterus down to the umbilical cord where it attaches to the placenta. A small amount of blood is taken for the test and the results are known with 4-5 days.
The risk of miscarriage is about 1%, the same as for the other procedures.
Fetal therapy
The Fetal medicine unit is able to carry out the following procedures in selected cases.
- Laser surgery for Twin-twin Transfusion Syndrome (TTTS)
- Laser surgery for selective intrauterine growth ristriction in monochorionic twins
- Umbilical cord occlusion for TRAP sequence (acardiac twin) and other discordant monochorionic twins
- Fetal shunt procedure for pleural effusion/ lung tumors and bladder outlet obstruction
- Intrauterine fetal blood transfusions
- Fetal tissue biopsy
- Diagnostic fetoscopy
More information on laser surgery for twin-twin transfusion syndrome
