Amniocentesis is the puncture of the amniotic sac using a fine needle in order to extract a small amount of amniotic fluid and fetal cells for study. It is for now the only 99.99% diagnostic method effective in the detection of numerical or structural pathologies of fetal chromosomes. Fetal cells can also be used to diagnose hereditary diseases inscribed in fetal DNA and the fluid can be used to look for markers of fetal infection in utero. In the near future fetal cells will be obtained from maternal blood and the use of this procedure will be considerably limited.

Genetic ultrasound has decreased the need for amniocentesis.

Let’s see the uses of amniocentesis:

1. Genetic amniocentesis: this is the most frequent use given to amniotic fluid. The fluid is placed in special media and the cells are cultured to obtain, after 2-3 weeks and after a biochemical and microscopic process, an image of the fetal chromosomes, the CARIOTIPE. This result is useful to detect numerical or structural chromosomal diseases that explain 0.3-0.6% of fetal anomalies.
2. Genetic tests: the cells of the amniotic fluid can be evaluated in search of heritable genetic diseases. These types of diseases are not seen in a chromosomal karyotype and require specialized tests on cellular DNA. The most used procedure is PCR, which detects genetic sequences of the affected DNA for each disease under study; each test costs around US $ 200.
3. Infections: through the bacteriological, viral or serological study of the amniotic fluid, the presence of infectious agents that could affect the baby can be detected.
4. Tests of fetal lung maturity: in many developed countries samples of amniotic fluid are obtained in search of biochemical data of lung maturity that help to make the decision of early interruption of complicated pregnancies.
5. Management of Rh incompatibility: in patients ORh (-) who have shown antibodies against the Rh (+) group of their baby, serial samples of amniotic fluid can be obtained to follow the evolution of the fetal condition and decide the type of treatment that You will receive the baby inside the womb. Every day is used less, the Rhogam has avoided many cases.
6. Uterine decompression: in cases of excessively dangerous accumulation of amniotic fluid, an important amount can be drained and discarded to favor the clinical condition of the patient and her baby.

How is the amniocentesis procedure?

With a long but very fine needle we puncture the maternal abdomen (and the pregnant uterus) until reaching the sac where the baby is surrounded by amniotic fluid. With an injector we extract a tiny portion of its contents, around 20 cc, and then remove the needle. The amniotic fluid is fetal urine with suspended fetal cells, the amount that is extracted is very scarce and does not commit the baby who urinating regains its original volume in 1 to 3 days.

Do I need a prior preparation?

Any.

Can the baby be hurt?

We introduce the needle under ultrasound surveillance following the path of the needle as it penetrates the maternal tissues to reach the space of amniotic fluid chosen for its volume, ease of entry and free of fetal parts: in good hands, it is practically impossible to injure a baby with the needle.

When should amniocentesis be done?

We usually do it from the 16th week of pregnancy since it is technically easier, cell cultures grow better and there is less risk of pregnancy loss. We tried to do it before week 18-20 since the final result takes 2 to 3 weeks, although in the Teaching Medical Center La Trinidad we have a very effective preliminary test that gives us the result in 24-48 hours (FISH, 99% sensitive) while we wait for the definitive one.

Does amniocentesis hurt?

In a research work, the expectation of pain before and after the procedure was evaluated and the results suggested that more than 98% of the patients reported less pain than they thought the procedure caused. The procedure is performed WITHOUT local anesthesia

Am I Rh (-) should I take any special foresight?

In these cases you should bring with you a vial of anti-Rh human antiglobulin (Rhogam) to be injected (to you) within the first 72 hours after the Amniocentesis.

Is amniocentesis better than echo or vice versa?

The genetic Amniocentesis only detects chromosomal problems while the echo can detect the vast majority of problems not related to the chromosomes (genetic problems and congenital malformations). In net numbers, ultrasound detects more anomalous conditions than Amnio because the vast majority of fetal problems do NOT have a chromosomal origin

What conditions does amniocentesis detect?

Alterations in the number and structure of chromosomes. The best known are: Trisomies (3 chromosomes) 21, 18 and 13, Monosomies (absence of a chromosome pair) such as Turner syndrome, alterations by multiplicity of sex chromosomes such as Klinefelter syndrome and alterations of the internal architecture of the chromosomes where large sections of DNA are gained or lost.

If I had exposure to toxins, chemicals or medications, should I get an amnio?

It is NOT indicated. Most exposures do not cause chromosomal damage or even congenital anomalies; In addition, normal or chromosomal abnormality is defined by the time of conception.

How are the results of genetic amniocentesis?

The result includes an enlarged microphotograph of the 46 chromosomes explaining the final diagnosis (female or normal male) and the technique used (band staining). The result must be endorsed by a recognized Geneticist. In recognized laboratories a normal result is 99.99% reliable. Click on the karyotype image to see a new colored form of Spectral Karyotype. Assign colors to the Chromosomes making their identification and classification easier (This case Normal male 46, XY)

Is the new method, the FISH, reliable?

It is very reliable (99%) but it does not evaluate many structural conditions of the chromosome, so it is always accompanied by a traditional karyotype as a definitive diagnosis.

Is the diagnosis of sex with amniocentesis safe?

100% sure. If the liquid is contaminated with maternal cells the result would indicate a female when the baby is a male. This rarely happens.

Why amniocentesis is practiced for mothers over 35 years of age?

The 35 years are established as a cut-off point since, starting at this age, the risk of pregnancy loss as a consequence of amniocentesis is similar to that of having a baby with a chromosomal problem; Here is the reason that would explain why Amniocentesis is not routine in younger or younger patients: because the risk of loss associated with the procedure outweighs the risk of having a baby with chromosomal problems.

But “Amnios” have also been made to young patients, why?

The following are indications of amniocentesis, regardless of age:

• Personal or family history of chromosomal problems.
• Ultrasonographic findings suggestive of chromosomal problems (first trimester genetic echo, for example).
• “Abnormal” laboratory findings in the blood risk test: Marking Triplet or Maternal serum markers.
• Management of the Rh (-) patient sensitized.
• Detection of fetal infections.
• Detection of genetic diseases.
• Maternal distress

Am I obliged to have an amniocentesis even if I have instructions?

No. The decision to practice an Amnio is for the patient and her partner.

What are the limitations of genetic amniocentesis?

It only serves to determine the presence of diseases associated with chromosomal disorders (0.3-0.6% of 3 to 6% of total problems at birth). If the baby has heart or digestive problems, joint deformities, metabolic diseases, mental retardation or any other problem without a chromosomal origin amnio will not detect it.