Prenatal testing is a way for doctors and expecting parents to gather information about the developing baby and either screen for or confirm the diagnosis of various congenital or chromosomal disorders. Amniocentesis, a test that involves analyzing the baby's DNA from an amniotic fluid sample, is the most accurate prenatal test for these serious conditions in the baby.
How the Test Works:
In an amniocentesis, a doctor uses ultrasound to direct a long needle through the mother's abdomen into the amniotic sac. The doctor collects a sample of the amniotic fluid around the baby. This fluid contains cells and DNA from the developing baby, which are then analyzed for common chromosome disorders.
Who Should Have an Amniocentesis:
Doctors usually recommend amniocentesis when a triple or quad screen blood test or a screening ultrasound has revealed higher than average odds for a chromosome disorder. In these cases, amniocentesis can provide a fairly reliable diagnosis. Amniocentesis is also sometimes offered routinely to all moms with higher risk for having a baby with a chromosome disorder, such as moms over 35 or those who carry genes that increase the risk for a serious inherited disorder.
What the Results Can Tell You:
Amniocentesis is more than 99% accurate for diagnosing chromosome disorders. False positives are rare. The test cannot give information on how severely affected the baby will be by the chromosome disorder, but a genetic counselor or perinatologist should be able to help you interpret the results of the test if the test reveals your baby has a genetic disorder.
Risk of Miscarriage:
Amniocentesis is controversial because some statistics are still circulating that claim the test has up to a 1% risk of causing a miscarriage, but research suggests that this figure is a high estimate and the true risk is closer to 1 in 400. Specialists who perform amniocentesis regularly will usually have post-procedure miscarriage rates far lower than the common estimates.
Other Uses for Amniocentesis:
In addition to confirming or ruling out genetic disorders, doctors can also use amniocentesis to evaluate the maturity of a baby's lungs in cases where premature delivery might be necessary for health reasons. Amniocentesis can also help doctors to monitor the baby's health in cases where the mother is sensitized to Rh factor.
Deciding Whether to Have an Amniocentesis:
It is important to point out that amniocentesis is not exclusively a test for Down Syndrome, a condition that causes developmental disabilities but usually not early death. Several other disorders can be diagnosed through amniocentesis, many of which have a more dismal prognosis than Down Syndrome.
Yet the mere mention of an amniocentesis can lead to heated debates among expectant parents. Many people feel that any added risk of miscarriage, no matter how small, is too great for a test that merely provides information. (There is usually no cure for disorders that can be diagnosed via amniocentesis.) Parents who are against abortion for any reason may be adamantly opposed to amniocentesis, feeling that the risk isn't worth it since they would not terminate a pregnancy for any reason. In contrast, others may prefer to terminate pregnancies affected by serious chromosome disorders, and thus they may choose amniocentesis so as to have a fairly reliable answer when there are signs that the baby may have a disorder. And regardless of parents' feelings on terminating pregnancies, some may choose an amniocentesis to confirm the presence of a suspected genetic disorder so that they can have adequate time to prepare for what lies ahead, rather than waiting until birth to find out whether the baby is healthy.
Amniocentesis. American Pregnancy Association. Accessed: March 10, 2009. http://www.americanpregnancy.org/prenataltesting/amniocentesis.html.
Amniocentesis. March of Dimes. Quick Reference: Fact Sheets. Accessed: March 10, 2009. http://www.marchofdimes.com/professionals/14332_1164.asp.