Amniotic Fluid Examination |
Also known as
Indications for amniocentesis
- The mother is 35 or older at the time of delivery. The probability
of fetal malformation increases with age. Up to 35, the increase in
probability is slow; but after 35, probability of fetal malformation
- The mother has delivered a baby with chromosome abnormalities.
- One of the parents is a balanced translocation carrier or has
abnormalities with chromosome structure.
- A close relative has Down Syndrome or other chromosome abnormality.
- There is a danger of Mendelian or polymeric genetic diseases such as
cleft lip, cystic fibrosis, and Tay-Sachs disease.
- In the past, children or parents have had a neural-tube defect, or
the mother's blood serum (fetoprotein or triple screen) test results were
- The fetus appears abnormal on ultrasound.
- Mother has given birth to a baby with multiple major malformations,
but has not received a cytogenetic examination.
- There is danger of a severe sex-linked genetic disease, and the sex
of the baby needs to be determined.
- A significant answer has been given to a genetic screening question.
- The mother is worried about fetal deformation and requests an examination.
Examining the amniotic fluid
Generally, it is ideal to perform or undergo an amniocentesis between
the 15th and 18th week of the pregnancy, when the success rate for
cultivating fetal cells is high. However, since it takes 3 weeks to
cultivate cells, abnormalities may not be discovered until the 5th month
of the pregnancy. Recently, early amniocentesis examinations have been
performed between the 11th and 14th weeks of gestation. An early
amniocentesis carries a 2.5 times higher risk of miscarriage than an
amniocentesis conducted during weeks 15 through 18.
How the fluid is examined
After the mother's abdomen is draped and prepped, a 3- to 6-inch needle
is used to penetrate the abdomen and uterus to collect amniotic fluid from
the amniotic sac. Approximately 20-30 ml is needed for cultivation, and
additional fluid may be collected for DNA analysis.
Complications with the examination
The three main dangers associated with amniocentesis are: injury to the
mother and fetus, infection, and miscarriage or premature labor.
(For mothers with Rh-negative blood who are bleeding, special precautions
and procedures will be necessary to avoid iso-immunization in the mother).
The chance of losing a baby from an amniocentesis performed during weeks
15 to 18 is approximately 1 in 200 to 1 in 300 procedures, similar to the
chance of losing a baby during this time if an amniocentesis was not
performed. Therefore, an amniocentesis performed during weeks 15 to 18 is
considered relatively safe.
Most pregnant women can safely undergo an amniocentesis. Special
circumstances that prevent the use of an amniocentesis are: if symptoms
of infection are present; if the woman refuses to undergo the procedure;
if danger of a premature birth exists.