1. Amniotic fluid sampling (amniocentesis)
Amniocentesis is a process through which we obtain a sample of amniotic fluid, present in the amniotic sac surrounding the fetus. The amniotic fluid contains cells derived from the embryo and these can be used to detect genetic or other fetal abnormalities.
Amniocentesis is usually performed after the 16th week until the end of the 3rd trimester. The physician uses a needle to draw a small amount of amniotic fluid under the guidance of ultrasound, in order to avoid injuring the fetus.
The risk of pregnancy loss and other pregnancy complications due to amniocentesis (procedure-related risk) is estimated to be less than 1/500 (0.2%) and this risk is of course directly related to the experience of the operator-physician.
Indications for performing amniocentesis include:
- fetal ultrasound abnormalities
- increased risk following combined 1st or 2nd trimester prenatal biochemical marker testing
- advanced maternal age (>35 years)
- parental anxiety – parental desire
- family history of a known genetic disease
- parent(s) carrier(s) of a chromosomal abnormality or of known gene mutations
2. Chorionic villi sampling (CVS)
Chorionic villi sampling was used for the first time in prenatal diagnosis in the late 1970s and early 1980s.
It is typically performed between the 11th and the 14th week of pregnancy. During sampling of chorionic villi, trophoblast cells and chorionic villi cells are drawn transcervically or transabdominally, depending on the placenta, the position of the uterus and the physicians assessment. Under ultrasound guidance, the operator removes a small sample of chorionic tissue, which is part of the placenta, with the aid of a small tube inserted through the cervix.
Chorionic villi cells are used to detect chromosomal abnormalities and/or for isolating DNA and diagnosis of a gene disorder in the fetus. The risk of pregnancy loss and other pregnancy complications due to chorionic villi sampling is estimated to be less than 1/100-1/200 (0.5-1%) and this risk is of course directly related to the experience of the operator-physician.
Indications for performing chorionic villi sampling include:
- abnormal ultrasound findings in the 1st trimester ultrasound scan (e.g. elevated nuchal translucency-NT)
- increased risk following combined 1st trimester prenatal biochemical marker testing
- family history of a known genetic disease
- parent(s) carrier(s) of a chromosomal abnormality or of known gene mutations
