Learn about the Amniocentesis test and its role in assessing the chromosomal structure of a baby.

Summary

  • Initial Report will be available within 10days and completer report by 4 weeks
  • There is a very minimal chance of miscarriage.
  • This sample is tested.
  • This is an invasive test, typically done between 16 and 20 weeks of gestation.
  • Gives a definitive answer whether the baby has a chromosomal disorder.
  • A sample of the fluid around the baby is extracted under ultrasound guidance
  • A doppler scan also helps check the low-resistance property of the uterine arteries that is how much they can be stretched.

What is amniocentesis?

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%)

Whyis amniocentesis recommended?

    It may be recommended for the following reasons:

  • If the patient is 37 years or older. Anyone can have a baby with a chromosomal abnormality, but the risk rises with the mother's age. For example, the likelihood of carrying a baby with Down syndrome rises from about1 in 1,200 at age 25 to 1 in 100 at age 40.
  • A pregnancy screening test has suggested there may be a problem, such as Down's syndrome, Edwards' syndrome or Patau's syndrome. 
  • The mother has had a previous pregnancy with these problems with Trisomy 21, 13 or 18.
  • An abnormality is detected in the baby during a routine ultrasound scan
  • To diagnose or rule out an intrauterine infection
    If too much amniotic fluid is accumulated (polyhydramnios), amnio reductionmight be done to drain excess amniotic fluid from the uterus.

What disorders and defects can amniocentesis detect?

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.

What is the risk of miscarriage from amniocentesis?

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

  • Cramps after the procedure.
  • Small amount of vaginal bleeding after the procedure.
  • Rarely, amniocentesis may cause amniotic fluid to leak.
  • Another rare complication is a uterine infection.A serious infection happens in about 1 in 1000 women (0.1%).
  • If the mother has an infection such as Hepatitis-C or HIV, amniocentesis can cause the infection to transfer to theunborn baby.
  • Needle injury - during amniocentesis the baby might move an arm or leg into the path of the needle. Serious needle injuries are rare and is usually taken care of,since it is ultrasound guided procedure.
  • Rh sensitization - rarely, amniocentesis might cause the baby's blood cells to enter the mother's bloodstream. If the mother has Rh negative blood and has not developed antibodies to Rh positive blood, the mother will be given an injection of a blood product called Rh immune globulin after amniocentesis. This will prevent the body from producing Rh antibodies that can cross the placenta and damage the baby's red blood cells. A blood test can detect if the mother has begun to produce antibodies.

How can the patient decide what's right for her?

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:

  • Opt for ultrasound-based screening and then make a decision about diagnostic testing (invasive procedures) based on the initial results.
  • Undergo diagnostic testing right away.
  • Have no screening or testing.

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.

How is amniocentesis performed?

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.

Is amniocentesis painful?

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.

How long does it take?

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.

Recovering after amniocentesis

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:

  • persistent or severe pain
  • a high temperature of 38C (100.4F) or more chills or shivering
  • discharge or clear fluid coming from the vagina
  • contractions (when your abdomen tightens then relaxes)
  • Loss of vaginal fluid or vaginal bleeding
  • Severe uterine cramping that lasts more than a few hours
  • Redness and inflammation where the needle was inserted
  • Unusual fetal activity or a lack of fetal movement

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