Amniocentesis (assessment exams)

Content

Introduction

Introduction

Amniocentesis consists in taking a small amount of amniotic fluid, the liquid that surrounds and protects the fetus in the uterus, to analyze it in the laboratory and build the chromosomal map of the fetus.

This allows us to ascertain the presence, or not, of any congenital anomalies (such as Down syndrome, Patau syndrome or Edwards syndrome) or genetic diseases (such as cystic fibrosis, Duchenne-Becker muscular dystrophy, thalassemia, phenylketonuria). More rarely, amniocentesis can be used to perform biochemical analyzes aimed at detecting metabolic errors and infectious diseases of the fetus.

It is carried out in the fourth month of pregnancy (between the 15th and 18th week) by introducing a needle through the maternal abdomen up to the inside of the uterus and, for this reason, it is a defined exam. invasive.

Amniocentesis is recommended: for women who have had a positive result in the prenatal screening test (combined test, bi test, tri test); for women who have had children with chromosomal diseases or neural tube defects, such as spina bifida; to women over the age of 35 who have not undergone first trimester screening tests; in case of family members (family history) with specific genetic diseases; in case of ultrasound results that suggest the presence of genetic diseases .

The results allow, in 99% of cases, to exclude or ascertain (diagnose) numerous genetic diseases, even if they cannot identify all of them. Regardless of the medical indications, the woman and her partner are free to decide whether or not to carry out the test, after talking to the doctor.

Amniocentesis involves an additional risk of abortion, less than 1%, compared to the risk of spontaneous abortion that every pregnancy has in itself. The experience of the doctor performing the examination can help reduce this risk, while performing the amniocentesis before the 15th week increases it.

In the third trimester, between the 32nd and 39th week of pregnancy, amniocentesis can be used to assess the maturation of the fetal lungs in women who are considering giving birth before the term of pregnancy.

The test

The test

Amniocentesis is performed in an outpatient clinic and does not generally require special preparation.

The woman is lying on her back with her abdomen uncovered.

The operator performing the examination checks the heartbeat, the position of the fetus and the placenta with ultrasound and identifies the best point to take the amniotic fluid.

After disinfecting the skin, the operator inserts a thin and hollow needle, under ultrasound guidance, through the abdominal wall until it reaches the uterus and the amniotic sac.

He then takes about 20 milliliters (ml) of amniotic fluid for subsequent analyzes, then removes the needle and checks the fetal heart rate again.

The withdrawal takes a few minutes, the whole procedure 30-45 minutes.

It is not a painful test, does not require any type of anesthesia, and women describe a discomfort similar to that of taking blood.

If the mother is of Rh negative blood type, anti-D immunoglobulin prophylaxis is recommended to prevent the formation of antibodies against the blood cells of the fetus.

After the amniocentesis it is recommended to stay at rest and avoid making efforts for at least 24 hours, following the instructions of your doctor.

If after the examination you experience loss of fluid or blood from the vagina, severe abdominal pain or cramps, fever, change in the perception of fetal movements (which are generally felt from the beginning of the fifth month), it is necessary to contact the attending physician immediately. .

The risks of amniocentesis, linked to the invasiveness of the procedure, include an additional risk of spontaneous abortion due to the examination which, today, is estimated to be less than 1%.

Other risks include uterine infections (less than 1 in every 1000 women who undergo the test) and vaginal bleeding which occurs in 2-3% of cases and almost always resolves spontaneously.

In the event of a recent amniocentesis, the appearance of a fever of an unclear nature should not be underestimated and a doctor should always be consulted.

Results

Results

To study the genetic heritage of the child through amniocentesis, different types of laboratory tests can be performed.

The faster tests, the results of which are available in a few days, allow you to know if there are problems due to alterations in the number of some chromosomes and allow you to ascertain (diagnose) the presence of Down syndrome (trisomy 21, caused by a chromosome 21 in excess), Edwards syndrome (trisomy 18, caused by an excess chromosome 18), Patau syndrome (trisomy 13, caused by an excess chromosome 13) and, if requested, to detect changes in the sex chromosomes.

If a more detailed examination of the chromosomes is required, which today makes it possible to ascertain the presence of a large number of diseases caused by submicroscopic gene alterations, it may take up to two or three weeks to obtain the answer of the examination.

The results provide a "yes" or "no" answer.

In most women who undergo an "amniocentesis, the result will be negative, ie it will indicate that the fetus is not affected by any of the genetic diseases investigated.

The positive result indicates, however, that the fetus has one of the diseases sought with the test. In this case the implications of the outcome will be discussed with the couple to help them assess what is the best decision to make.

Unfortunately, no treatment is available for most genetic diseases.

If you decide to continue the pregnancy it is advisable to enlist the help of health professionals to choose the most suitable place for the birth and to arrange any specific treatments for the baby's needs.

If you decide to terminate the pregnancy, by means of a therapeutic abortion, you will receive information on where and how to carry out the surgery based on the week of pregnancy.

In 1 case out of 100 it may happen that the result of the examination is not clear and it is necessary to repeat the procedure.

Before undergoing prenatal assessment (diagnosis) techniques, such as amniocentesis or CVS, there is an interview with a physician expert in medical genetics who provides the couple with detailed information on:

  • pathologies that can be ascertained (diagnosed) with amniocentesis and CVS
  • test (amniocentesis or CVS) recommended in your case
  • available laboratory tests and the significance of the results
  • reliability of laboratory tests
  • risk of having an uncertain result and having to repeat the procedure
  • risk of abortion related to the examination, including that detected in the clinical center where the test will be performed
  • time to get results
  • options available if the fetus has one of the genetic conditions sought by the test
Bibliography

Bibliography

Akolekar R, Beta J, Picciarelli G, Ogilvie C, D "Antonio F. Procedure-related risk of miscarriage following amniocentesis and chorionic villus sampling: a systematic review and meta-analysis. Ultrasound in obstetrics and Gynecology. 2015; 45: 16–26

Salomon LJ, Sotiriadis A, Wulff CB, Odibo A, Akolekar R. Risk of miscarriage following amniocentesis pr chorionic villus sampling: systematic review of literature and updated meta-analysis. Ultrasound in obstetrics and Gynecology. 2019; 54: 442–451

NHS fetal anomaly screening program (FASP). FASP: parent information on screening for conditions (English)

Royal College of Obstetricians and Gynaecologists (RCOG). Amniocentesis and Chorionic Villus Sampling. RCOG Green Top Guideline. 2010; 8

American College of Obstetricians and Gynaecologists "Committee on Practice Bulletins - Obstetrics, Committee on Genetics, Society for Maternal-Fetal Medicine. Practice Bulletin n.162: Prenatal diagnostic testing for genetic disorders. [Summary]Obstetrics and Gynecology. 2016; 127 (e): e108-e122

Alfirevic Z, Navaratnam K, Mujezinovic F. Amniocentesis and chorionic villus sampling for prenatal diagnosis. Cochrane Databases of Systematic Reviews. 2017; 9: CD003252

In-depth link

In-depth link

Saperidoc. Prenatal diagnosis of genetic diseases

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