Genetic amniocentesis is a diagnostic procedure performed in the early second trimester that involves collection of amniotic fluid from within the uterine cavity.

What are the indications for genetic amniocentesis?
Genetic amniocentesis is most commonly performed for evaluation of fetal karyotype (chromosomes) or amniotic fluid alpha-fetoprotein (AFP) concentration.

The most common indicators for performing fetal karyotype evaluation are

• increased risk of fetal chromosomal abnormalities associated with advanced maternal age (AMA)
• abnormal second trimester maternal serum screening.

The most common indication for evaluation of amniotic fluid AFP is

• abnormal second trimester maternal serum screen with increased maternal serum AFP indicating an increased risk of fetal open neural tube defect (ONTD)
• spina bifida.

Other indications for genetic amniocentesis include

• history of a previous pregnancy or child with chromosomal abnormality,
• family history of a chromosomal abnormality or other genetic disease / syndrome,
• parental chromosomal abnormality,
• family history of inherited metabolic abnormalities for which prenatal diagnosis is available,
• abnormal fetal growth,
• when fetal abnormalities are identified by prenatal ultrasound.

When is genetic amniocentesis performed?
Genetic amniocentesis is most commonly performed between 15 and 18 weeks of gestation, but can be performed any time after 15 weeks. The risks of the procedure may differ depending on the gestational age at the time of testing.

How is genetic amniocentesis performed?

• Genetic counseling is provided prior to finalizing a decision regarding genetic amniocentesis testing.
• A detailed ultrasound is performed for evaluation of fetal and maternal anatomy, and evaluation of the placental implantation sight.
• The procedure is performed using a small needle that is inserted into the uterus through the lower abdominal wall for withdrawal of a small amount of amniotic fluid.
• The needle insertion is accomplished using ultrasound guidance.
• The amniotic fluid is sent to a laboratory for evaluation of fetal karyotype (chromosomes), AFP concentration, and any other indicated tests.

When are the results of genetic amniocentesis available?
The time to obtain final results will vary by type of test performed:

• Chromosome testing following tissue culture are generally received within 10-12 days of the procedure.
• Amniotic fluid AFP results are generally available within 5-7 days of the procedure.
• Results of testing for other genetic diseases may take a longer period of time; this generally depends on the type of testing requested
• Preliminary results for some chromosomal abnormalities may be obtained earlier using specialized laboratory techniques such as fluorescent in situ hybridization (FISH).

What are the advantages of genetic amniocentesis testing as compared to chorionic villus sampling (CVS)?
The principle advantage of amniocentesis testing is the ability to evaluate amniotic fluid AFP concentration.

What are the risks of genetic amniocentesis?
The procedure related pregnancy loss risk of genetic amniocentesis is 0.5% or less. The risk of premature rupture of membranes is approximately 1% or less.