After the 1^st trimester screening is performed, the patient receives the calculation of risk showing the probability of that baby having a chromosomal or genetic problem (i.e. Down Syndrome). In low risk cases, prenatal care follows as usual. In high risk cases (>1:100 or presence of major defects), the patient/couple is offered to be submitted to a diagnostic test.

The diagnostic tests aim to obtain and analyze the feus genetic material in order to confirm or refute the suspicion of problems. They deliver a sure result regarding chromosomal defects and some genetic syndromes. There are 2 types of invasive tests: chorionic villus sampling and amniocentesis.

Chorionic villus sampling

Chorionic villus sampling (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.

*There are rare cases in which there is discordance between the genetic material of placenta and fetus. In such cases, amniotic fluid analysis is necessary.

How is CVS done?

Local anesthetic is given. A fine needle is then passed through the mother’s abdomen and uterus and a sample of villi is taken. The needle is carefully observed using ultrasound scan.

The procedure lasts around 1 minute and afterwards we check that the fetal heartbeat 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 most cases the pregnancy continues without any problems.

If there is a lot of pain or bleeding or if you develop a temperature, please seek medical advice.

When can I expect to get the results?

The results for Down’s syndrome and other major chromosomal defects are usually available within 3 days. The results for rare defects take 3/4 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 because 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 five days.

Some studies have shown that when CVS is performed before 10 weeks there is a small risk of abnormality in the baby’s fingers and/or toes. To avoid this risk, we never perform CVS before 11 weeks.

Amniocentesis

Amniocentesis involves the examination of cells in the fluid from around the fetus (amniotic fluid).
The cells in the amniotic fluid originate from the baby and so the chromosomes present in these cells are the same as those of the baby.

How is amniocentesis done?

• Amniocentesis involves passing a thin needle into the uterus in order to remove a small volume of amniotic fluid. The needle is carefully observed using ultrasound scan.
• The fluid is fetal urine and the amount removed by amniocentesis reaccumulates within a few hours.
• The procedure lasts 1 minute and afterwards we check that the fetal heartbeat is normal.

What should I expect after amniocentesis?

• For the first couple of days you may experience some abdominal discomfort or period-like pain.
• If there is a lot of pain, bleeding, loss of fluid from your vagina or if you develop a temperature please seek medical advice.

When can I expect to get the results?

• The results for Down’s syndrome and other major chromosomal defects are usually available within 3 days. The results for rare defects take 3-4 weeks. As soon as we get the results, we will call you to let you know

What are the risks associated with amniocentesis?

• The risk of miscarriage due to amniocentesis is about 1% and this is the same as the risk from chorionic villus sampling. If you were to miscarry due to the test, this would happen within the next five days.
• Some studies have shown that when amniocentesis is performed before 16 weeks there is a small risk of the baby developing club feet. To avoid this risk, we never perform amniocentesis before 16 weeks.