Amniocentesis is a diagnostic test whereby amniotic fluid is removed from the uterus for analysis or treatment.
While can provide valuable information about the health of the baby with minimal risk, the possibility of abortion exists (0.6 percent from the 15th week of gestation), so it is logical for the woman to consider whether or not to perform it if her gynecologist recommends it if she sees possible changes in the previous screening tests.
We answer the most common questions that arise around amniocentesis, to have all the data before making a decision.
What is amniocentesis?
His name comes from 'amnion', the bag that encloses the amniotic fluid, and 'centesis', which means prick.
And it is that this prenatal test consists of the extraction of the amniotic fluid that surrounds the fetus and that allows it to move within the wall of the uterus comfortably. In addition, it contains other components necessary for the growth of the child and cells detached from his body.
In short, amniocentesis refers to the procedure of puncturing and absorbing with a needle some amniotic fluid through the mother's belly and then analyzing it.
When is it recommended?
The Mayo Clinic explains that amniocentesis can be done for several reasons:
Genetic testing To detect certain chromosomal abnormalities, such as Down syndrome.
Maturity test of the baby's lungs. Analyze the amniotic fluid to determine if the baby's lungs are mature enough for birth.
It is only done if premature labor is being considered (either by induction or by caesarean section) in order to prevent pregnancy complications for the mother in a non-emergency situation. It is usually performed between weeks 32 and 39 of pregnancy. It is unlikely that the baby's lungs are fully developed before week 32.
Diagnosis of a fetal infection. Or to assess the severity of anemia in babies who have Rh sensitization, a rare disorder in which the mother's immune system produces antibodies against a specific protein on the surface of the baby's blood cells.
Polyhydramnios treatment. When too much amniotic fluid accumulates in the uterus during pregnancy, an amniocentesis may be done to drain the excess.
Genetic amniocentesis: the most common
Until a few years ago, amniocentesis was recommended for all women over 35 or 38 years old (depending on the autonomous community), taking into account that the risk of chromosomal abnormalities increases with age.
Today however it is possible to avoid a significant number of amniocentesis by defining the risk with the markers that are obtained with different screening tests: maternal blood biochemical test (combined first trimester test), fetal DNA test and ultrasound.
They are included in the prenatal diagnostic programs of the different Spanish health systems and allow us to know with high reliability (85-90%) the risk of suffering from chromosomal abnormalities.
In this way, health networks advise an invasive test such as amniocentesis only to pregnant women who obtain a combined test report with a high risk result (greater than or equal to 1 between 250-350, depending on the cut established by each autonomy ) and to whom:
Have had a chromosomal disorder or a neural tube defect in a previous pregnancy. If a previous pregnancy was affected by disorders such as Down syndrome or a neural tube defect (a serious disorder that affects the brain or spinal cord), your doctor may recommend amniocentesis to confirm or rule out these disorders.
Have a family history of a genetic disease specific or if the father or mother are known carriers of a genetic disease, such as cystic fibrosis.
They have abnormalities on some ultrasound.
In Babies and more A new blood test can diagnose genetic disorders from the first weeks of pregnancy In which week of gestation is it performed?
Cochrane reviews, which consist of an exhaustive analysis of existing medical evidence, have revealed that Amniocentesis is safer between sixteen and eighteen weeks gestation.
In any case, as the Mayo Clinic warns, amniocentesis is not suitable for all cases. The doctor may advise against amniocentesis if the woman has an infection. (such as HIV, hepatitis B or hepatitis C), since these infections can be transmitted to the baby during amniocentesis.
Amniocentesis is included as a protocol test, and therefore free, in the public health network of Spain, both for pregnant women who have been diagnosed with high risk, and for those who claim anxiety about any abnormality.
This is done, step by step
- Before. If the amniocentesis is done before the 20th week of pregnancy, it may be necessary for the woman to have to drink a lot of fluid to have the uterus sustained. However, after the 20th week of pregnancy the bladder should be empty to minimize the chance of inaccurate puncture.
It will be the doctor who explains the procedure to the mother, who must sign a consent.
Ultrasound The woman lies on her back on a stretcher with her abdomen exposed and the specialist applies a special gel on the abdomen and then uses a small device known as an "ultrasound transducer" to know the exact position of the baby on a monitor.
Insert a needle. After cleaning the abdomen with an antiseptic and, guided by ultrasound, you will insert a thin, hollow needle through the abdominal wall, until you reach the uterus.
Remove the liquid. With a syringe, the doctor will remove a small amount of amniotic fluid and then remove the needle. The amount of fluid depends on the weeks of pregnancy.
The mother should remain still while the needle is inserted and the amniotic fluid is removed.
Does amniocentesis hurt?
Each person has a pain threshold, and unique factors such as nerves, make each case different.
But the process is so gentle that the use of local anesthesia is not indicated. The area in which one works is not especially populated by nerves responsible for nociception (the perception of pain) so it is hardly perceived physiologically.
Even so, it is convenient for the mother to come with the test, both for the emotional support she provides, and for taking her home.
Should we rest after the test?
Despite being an invasive test, its physiological impact is minimal. That means the mother could return to normal activity immediately.
However, it is recommended to rest for forty-eight hours after the test to avoid fluid loss or possible complications, and refrain from sexual intercourse, at least the first day.
In addition, the woman may experience spasms or mild pelvic discomfort after an amniocentesis.
You have to go to the emergency room in case of:
Loss of vaginal secretions or vaginal bleeding
Severe uterine spasms that last more than a few hours
Fever
Redness and inflammation where the needle was inserted
Unusual fetal activity or lack of fetal movement
What risks does the test entail?
As the Mayo Clinic explains:
- Loss of amniotic fluid. Exceptionally, after an amniocentesis, the amniotic fluid can be filtered through the vagina. However, in most cases, the amount of fluid lost is small and stops within a week.
In those cases you can choose to hospitalize the pregnant woman to control her until she recovers.
Spontaneous abortion. Amniocentesis during the second trimester carries a small risk of spontaneous abortion, approximately 0.6 percent, somewhat higher if performed before week 15.
Injury caused by the needle. They are very rare, although it may happen that the baby moves an arm or leg in the path of the needle.
Sensitization to Rh factor. Exceptionally, amniocentesis could cause the baby's blood cells to enter the mother's bloodstream.
If the woman is Rh negative and did not develop antibodies against the blood of the Rh positive group (which is checked by an analysis), she will be given an injection of a blood derivative called "Rh immunoglobulin" after the test.
This will prevent your body from producing anti-Rh antibodies that could cross the placenta and damage the baby's red blood cells.
- Transmission of infection to the baby. Very unlikely, because amniocentesis is not done if the woman has hepatitis C, toxoplasmosis, HIV or AIDS, the infection could be transmitted to the baby during amniocentesis.
In Babies and more Amniocentesis, a confirmationAnalysis of the results
The sample of extracted amniotic fluid will be analyzed in a laboratory. Some results may be available in 24-48 hours. Others could take up to four weeks.
In case of genetic diagnosis, it is necessary to keep the cells obtained in culture for 14 days. That means that the woman must wait between three and four weeks on average since the test was performed to know the result.
Are there early diagnosis alternatives?
To rule out or detect fetal problems as soon as possible, you can opt for chorion biopsy. It can be done from the tenth week of gestation and the result is obtained in 24-48 hours. It consists of obtaining chorial villi of the developing placenta and is performed by abdominal or vaginal puncture, depending on the week of gestation and the position of the placenta. The problem is that it is also an invasive test with an estimated risk of abortion between 1% and 2%.
Conclusion: Amniocentesis is an invasive test with minimal but existing risks (0.6% chance of abortion). It is not a mandatory diagnostic test although it is protocol and free in Social Security, recommended in case of irregularities in the combined prenatal screening or if there is a history of genetic problems.
If detected early, they could help treat possible changes in the fetus (such as spina bifida) as soon as possible and improve the diagnosis.
So it is most convenient to assess the pros and cons with the gynecologist before deciding whether to do it or not.
Photos | iStock
