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
- spina bifida.
Other indications for genetic
- history of a previous
pregnancy or child with chromosomal abnormality,
- family history of a chromosomal
abnormality or other genetic disease / syndrome,
- parental chromosomal
- family history of inherited
metabolic abnormalities for which prenatal diagnosis is
- abnormal fetal growth,
- when fetal abnormalities
are identified by prenatal ultrasound.
When is 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
- Genetic counseling is
provided prior to finalizing a decision regarding genetic
- 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
When are the results of genetic
The time to obtain final results
will vary by type of test performed:
following tissue culture are generally received within
10-12 days of the procedure.
results are generally available within 5-7 days of the
- 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
advantage of amniocentesis testing is the ability to evaluate
amniotic fluid AFP concentration.
What are the risks of genetic
related pregnancy loss risk of genetic amniocentesis is
0.5% or less. The risk of premature rupture of membranes
is approximately 1% or less.