Invasive Procedures
Examples of cases when an invasive test is required is when there is increased risk for chromosomal abnormality, such as Down syndrome or a anomaly has been diagnosed during the ultrasound examination or the pregnancy is at risk for a genetic condition (such as β-thalassemia).
CVS-Chorionic Villous Sampling
Chorionic villus sampling (CVS) is performed at the end of the first trimester of the pregnancy (11 weeks and after). Similarly to all invasive procedures a thin needle is introduced to the womb under ultrasound guidance. The needle is directed to the placenta (called at this early stage the trophoblast) and a small sample is taken for further analysis. Genetic tests in the placenta reflect the baby’s genetic condition as the placenta and the baby share the same genetic make up.
The sample is examined in a genetic laboratory. The procedure is done under local anesthetic and takes a few minutes. The additional risk of miscarriage attributed to the procedure is about 1-2 in 1000 pregnancies.
Amniocentesis
Amniocentesis is performed from the 16th week onwards. A thin needle is introduced under ultrasound guidance in the sac of the pregnancy and amniotic fluid is drawn. The procedure takes a few minutes. The amniotic fluid is fetal urine and contains cells derived from the baby’s kidneys, lungs and skin.
The fluid is examined in a genetic laboratory.
The risk of miscarriage attributed to the procedure is about 1-2 in 1000 pregnancies.
Fetal blood sampling
In rare cases there is a need to perform special tests in the baby’s blood. The procedure involves the introduction of a thin needle in the umbilical cord of the baby. The risk of miscarriage depends on the fetal condition and is about 5%.
Embryo reduction in multiple pregnancy
Multiple pregnancies have an increased risk for complications such as miscarriage and preterm delivery. Reducing the number of fetuses can lower some of the risks.
The procedure is performed under ultrasound guidance usually at the end of the first trimester after detailed ultrasound examination and assessment of the risk for abnormality in each fetus. Embryo-reduction can also be performed later in cases of a severe anomaly in one of the fetuses of a multiple pregnancy.
