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Amniocentesis is a prenatal test that allows the fetal medicine specialist to gather information about the baby's health from a sample of the fluid that surrounds the baby in the uterus. This fluid is called the amniotic fluid. Amniotic fluid contains skin cells shed from the baby and is used to diagnose chromosomal abnormalitis such as Down syndrome.
Amniocentesis produces a karyotype – a picture of thebaby's chromosomes – to determine if there are any abnormalities. (In about 1 percent of cases, there's a problem with the specimen and the test doesn't yield a result.)
Amniocentesis is usually done when a woman is between 16 and 20 weeks pregnant. Though all women have the option of having an amniocentesis, women for whom this test is recommended are often those at increased risk for genetic and chromosomal problems.The test is invasive and carries a small risk of miscarriage (0.01%)
It may be recommended for the following reasons:
Amniocentesis is used to detect nearly all chromosomal disorders, including Down syndrome, trisomy 13, trisomy 18, and sex chromosome abnormalities (such as Turner syndrome). While the test can diagnose these conditions it can't measure their severity.
It can also detect several hundred other genetic disorders, such as cystic fibrosis, sickle cell disease, and Tay-Sachs disease. The test is not used to look for all of them, but if thebaby is at increased risk for one or more of these disorders, amniocentesis can usually tell whether the babyhas the disease.
The risk of miscarriage due to amniocentesis is low. Because a certain percentage of women will end up miscarrying in the second trimester anyway, there's no way of knowing for sure whether a miscarriage following an amniocentesis was actually caused by the procedure.
Estimates vary, but research suggests that the loss rate from the procedure is around 1 in 100 to 200.
Before the patient decides to have amniocentesis, the risks and possible complications will be conveyed by the doctor.
There are also some other risks, such as infection or needing to have the procedure again because it wasn't possible to accurately test the first sample that was removed.
The risk of amniocentesis causing complications is higher if it's carried out before the 15th week of pregnancy, which is why the test is only carried out after this point.
Other risks include
First and second-trimester screening as well as diagnostic testing optionscan only be recommended by doctors, but whether or not to test is a personal decision of the mother and her family.
Some possible choices are:
If the patient opts for screening first, she can then decide — with the help of the doctor — whether the results indicate a high enough risk that a CVS or amniocentesisis required to confirm whether a problem exists. The patient willneed to weigh the need to know about thebaby's condition against the small chance that diagnostic testing could cause a miscarriage.
There are a few conditions that may be detectedwhile the baby is still in the womb. So if there's a strong suspicion that the baby may have one of these rare problems, an amniocentesiscan help find out.
The procedure usually takes about 15 minutes. Before the procedure, an ultrasound is done to measure the baby and check the basic anatomy.
For the procedure itself, the abdomen is cleaned with sterile solution to minimize the risk of infection. Ultrasound is used to pinpoint a pocket of amniotic fluid a safe distance from both the baby and the placenta. This part can take up to 10minutes.
Then, under continuous ultrasound guidance, the doctor inserts a long, thin, hollow needle through the abdominal wall and into the sac of fluid around the baby. The doctor withdraws a small amount of amniotic fluid and then removes the needle. Sometimes, not enough fluid is removed the first time the needle is inserted. If this happens, the needle will be inserted again.Withdrawing the fluid can take a few minutes but usually takes less than 30 seconds. The baby will make more fluid to replace what's taken out.
The amniotic fluid, which contains cells shed by the baby, is sent to the laboratory for analysis. First level of reporting (initial confirmation) will be available in 10 to 15 days and the final report will be available in 4 weeks time.
Afterward, the doctor may use an external fetal monitor to listen to the baby's heartbeat for reassurance.
Amniocentesis isn't usually painful, but the patient may feel uncomfortable during the procedure.
Some women describe experiencing a pain similar to period pain or feeling pressure when the needle is taken out.
The patient may sometimes feel some cramping, pinching, or pressure during the procedure. The amount of discomfort or pain varies among women and even from one pregnancy to the next.
The procedure usually takes around 15 minutes to perform.
Afterwards, the patient will be monitored for up to an hour, in case the test causes any side effects, such as heavy bleeding.
After amniocentesis, it's normal to have cramps similar to period pain and light vaginal bleeding called "spotting" for a day or two.
It is advised to avoid any strenuous activity for a few days following the procedure.
However the patient should contact the obstetricianin case of the following symptoms: