Amniocentesis is a test that can reveal certain fetal abnormalities. Amniotic fluid is obtained for study from the fluid surrounding the fetus. The amniotic fluid must be withdrawn by needle. Ultrasound is used to locate a pocket of fluid where the fetus and placenta are out of the way. Skin over the abdomen is cleaned and numbed with a local anesthetic. A long needle is then passed through the abdomen into the uterus, and fluid is withdrawn from the uterus with a syringe.
Amniocentesis does not need to be performed on every pregnant woman. It is usually offered to women
|who will deliver after their 35th birthday
|who have had a previous baby with a birth defect
|with a family history of birth defects
|who have a birth defect themselves
|whose partners have a birth defect
This test is usually performed for prenatal evaluation between 16 and 18 weeks of pregnancy. Some doctors are using amniocentesis at 11 or 12 weeks of pregnancy; however, risks are higher when it is done at this time. A study in the medical journal Lancet reports that miscarriage and a higher incidence of babies born with a clubfoot have been noted.
Only about 1 ounce (30ml) of amniotic fluid is needed to perform tests. Fetal cells that float in the amniotic fluid can be grown in cultures. These cells are used to identify fetal abnormalities or to reassure you that your baby is healthy.
We know of more than 400 abnormalities a child can be born with. Amniocentesis can identify about 40 problems. The problems a physician can identify include the following:
|chromosomal problems, particularly Down syndrome
|skeletal diseases, such as osteogenesis imperfecta
|fetal infections, such as herpes or rubella
|central-nervous-system disease, such as anencephaly
|blood diseases, such as erythroblastosis fetalis
|chemical problems or deficiencies, such as cystinuria or maple-syrup-urine disease
Amniocentesis can determine the baby's sex. However, the test is not used for this purpose, except in cases in which the sex of the baby could predict a problem, such as hemophilia. It may also be used later in pregnancy to determine if the baby's lungs are mature.
Risks are relatively small; fetal loss from complications is estimated to be between 0.5 and 3%. Discuss the risk with your doctor before you have the test.
Who Performs Amniocentesis?
The test should be performed only by someone with experience doing it, such as a physician at a medical center. Your healthcare provider can give you more information if the test is to be performed on you.
About Down Syndrome
Down syndrome is a condition caused by an extra chromosome. A baby is mentally retarded and may have a somewhat dwarfed appearance, with a sloping forehead, short, broad hands, a flat nose and low-set ears. He or she may also have heart problems, gastrointestinal defects or leukemia. Down syndrome can be diagnosed during pregnancy by amniocentesis.
Other tests that can help diagnose Down syndrome include alpha-fetoprotein (AFP), the triple-screen test, chorionic villus sampling and ultrasound (in some cases). Amniocentesis or chorionic villus sampling (CVS) is done to confirm the diagnosis when "screening tests" such as AFP indicate a potential problem.
Bringing Others to Your Prenatal Appointments
It's a great idea to bring your partner along to a prenatal appointment! It will help him realize what is happening to you and to feel a part of the pregnancy. And it's nice for your partner and your doctor to meet before labor begins.
It's also all right to take your mother or mother-in-law to an appointment with you to hear the baby's heartbeat. Things have really changed since your mother carried you; she might enjoy a visit. If you want to bring anyone else, discuss it with your healthcare provider first.
Children at prenatal appointments.
Many offices don't mind if you bring your children with you; other offices ask that you not bring children along. Ask about office policy. If you're having problems and need to talk with your doctor, it can be difficult to talk if you're also trying to take care of a young child.
Suggestions for bringing children along.
Suggestions for bringing children to an office visit include the following:
|Ask about office policy ahead of time.
|Don't bring them on your first visit, when you will probably be having a pelvic exam.
|If you're bringing your children to hear the heartbeat, don't bring them the first time your doctor tries to hear it; wait until after you have heard it first.
|Bring one or two children at a time rather than a large group.
|Bring something to entertain your child in case you have to wait—not all offices have toys or books for kids.
|Be considerate of other patients; don't bring a child who has a cold or is sick. I've had patients bring their children with them, then tell me the child had chickenpox or strep throat! This could be very serious for other pregnant women sitting in the waiting room.
|Don't bring other people's children to your appointment.