Amniocentesis Health Article

Amniocentesis

A medical test that involves withdrawing a sample of fluid from the amniotic sac surrounding the fetus in the abdomen of the pregnant woman.

Amniocentesis is a procedure used to detect the presence of genetic disorders such as Down syndrome and spina bifida in a fetus. The primary tool for prenatal diagnosis, it is also used to determine the maturity level of a potentially premature baby. Amniocentesis is normally performed in the 14th-16th weeks of pregnancy in women considered to be at risk of Down syndrome or other problems.

Prior to the development of amniocentesis in the 1950s, there was no way to detect whether a baby might be born with serious health problems. Amniocentesis has changed the nature of pregnancy by offering greater information about the fetus and creating more decisions for the parents. If problems exist with the fetus, the pregnant woman must decide if she will continue the pregnancy.

Amniocentesis takes advantage of a wealth of 20th-century technological and medical advances in genetics, fetal development, and diagnostic testing knowledge. The procedure is performed by inserting a hollow needle through the abdominal and uterine walls into the amniotic sac. The fluid in the amniotic sac is rich with cells from the fetus, and approximately half an ounce of amniotic fluid is removed.

The fluid is placed in a centrifuge that divides the cells from the liquid. The amniotic liquid and the cells are then analyzed. The amniotic fluid is examined to determine the level of alpha fetoprotein, a chemical normally present in the blood. High levels of alpha fetoprotein suggest a possible spinal-cord defect such as spina bifida, while low levels of the chemical suggest the possibility of Down syndrome.

The cells, called amniocytes, may also be examined for genetic abnormalities or inborn metabolic errors. Some problems can only be detected after the cells are cultured (the process of growing cells in a laboratory in special material that encourages cell growth).

Amniocentesis is not without some risk to the fetus. About 0.5% of all amniocentesis procedures cause spontaneous abortions. Other possible complications include injury to the fetus and infection of the fetus or the mother. Another disadvantage of the procedure is that it cannot be performed until the 14th week of pregnancy, when the symptom is already well established. Test results cannot be reported for two weeks.

The most common genetic abnormality detected with amniocentesis is Down syndrome. Down syndrome occurs when children are born with 47 chromosomes in each cell instead of the normal 46. Children with this syndrome are mentally retarded and are more likely to have congenital heart disorders and other health problems. Women are at greater risk of giving birth to a Down syndrome child as they grow older. Women 35 and over are generally advised to have an amniocentesis when they are pregnant because the risk of having a Down syndrome child is higher than the risk of losing a baby due to amniocentesis at this stage.

Spina bifida, a serious disorder in which the spine develops abnormally, is another health problem that can be detected by amniocentesis. Spina bifida usually causes some paralysis and may cause other physical disabilities. Inborn metabolic disorders detected by amniocentesis include Tay-Sachs disease, a genetic disorder that causes blindness and paralysis. It is fatal in infancy.

Couples at risk for other health problems are also advised to have an amniocentesis. This includes men or women who already have a child with a chromosome abnormality, neural tube defect, or metabolic disorder. A family history of certain genetic problems may also prompt some pregnant women to have an amniocentesis.

The long-term outlook for children born following amniocentesis is positive. A Canadian study compared the health of 1,298 children who had experienced amniocentesis before birth with 3,738 children who had not experienced the procedure. The study, which examined children ages 7-18, found no higher incidence of any health problems in the children who had undergone an amniocentesis.

Experts disagree about whether pregnant women younger than 35 should have amniocentesis. Only 25% of the women who give birth to Down syndrome babies are 35 or older, which means most Down syndrome infants are born to women younger than 35. Some experts have suggested that women 30 and over should have amniocentesis.

Another dispute concerns whether amniocentesis should be used as a tool to select the sex of a fetus. Opinion on the issue has changed among genetics counselors who advise potential parents about genetic testing. In 1975 only 1% of a physicians and technologists polled reported that they would perform amniocentesis for the purpose of sex selection. By 1988 a total of 62% said they would perform the procedure for this purpose.

As knowledge of genetics increases, the scope of information provided through amniocentesis should also increase, creating more choices for pregnant women and their families. Critics say amniocentesis and other prenatal tests have changed pregnancy from a seamless nine months of preparation to a time of uncertainty and important decision-making. While this may be true, amniocentesis has also provided tools for the healthy birth of many infants, including many born to parents whose genetic heritage would have made the birth of healthy offspring unlikely.