Amniocentesis
Many women have amniocentesis performed, but it is not a routine procedure. It is offered between 15 and 20 weeks gestation to a pregnant woman when:
she is 35 years of age or older;
there is a strong family history of a genetic disorder;
both parents possess a gene for an inherited disorder; or
the level of maternal alpha-fetoprotein (AFP) is either lower or higher than expected.
Amniocentesis may also be performed after 32 weeks of gestation to help assess the degree of lung development for babies that are at risk of a premature delivery.
Amniocentesis is a procedure used to obtain a small amount of amniotic fluid, which contains AFP produced by the baby and fetal cells. The fetal cells can be tested for chromosomal or genetic abnormalities. A gene analyses may be performed based on family history (i.e., another child born with a defect or with a hemoglobinopathy) or on the results of screening tests performed on the parents (such as for Cystic Fibrosis). Approximately two weeks are needed to complete the testing.
Risks associated with amniocentesis:
There is a slight risk that the needle inserted into the amniotic sac may puncture the baby, cause a small amount of amniotic fluid leakage, cause an infection, and in rare cases may cause a miscarriage.
Limitations of amniocentesis:
An elevated amniotic fluid AFP is not conclusive for neural tube defects.
For certain genetic tests, there is greater reliability of results when testing individuals that are of an ethnic background with a higher prevalence of specific genetic abnormalities.
Not all genetic disorders can be detected.
