Amniocentesis during pregnancy: timing and indications for the procedure

How is amniocentesis done?

This invasive procedure is performed using a syringe connected to a long, hollow needle. It punctures the abdominal wall, uterus and amniotic membrane, after which a sample of amniotic fluid is “pulled” through it with a syringe or, conversely, a medicinal solution is injected.

The procedure is carried out in two ways:

Free hand method.
The puncture is carried out under ultrasound control, with the help of which the area of needle insertion is specified. It is selected in such a way that there is no placenta in this place or its wall has a minimum thickness. This avoids possible complications and reduces the risk of damage to the fetus.
Using an adapter.
The difference between this method is the pairing of the needle with an ultrasound sensor, with the help of which the trajectory of its movement is first calculated depending on the insertion in a particular place. At the same time, the doctor performing the procedure has the opportunity to observe the needle itself and its trajectory, thereby choosing the most optimal route for its advancement. However, even in this case, the operation requires highly qualified and experienced surgeons.

The total duration of the procedure including preparation is approximately 5 minutes. Of these, 1 minute is spent on the puncture, and the remaining time is taken to collect amniotic fluid and remove the needle. For 2 hours after the operation, the patient rests and is under the supervision of a doctor to avoid possible complications. To reduce pain during the puncture, local anesthesia can be used. However, doctors recommend doing without it - the pain from an anesthetic injection is in no way inferior to that of the operation itself. In addition, the anesthetic may cause individual intolerance.

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Complications and consequences of lumbar puncture

In the first 2-3 hours after the procedure, the patient should be in a horizontal position; some discomfort is possible - for example, a headache after a lumbar puncture, which quickly disappears and does not require the use of painkillers. You should not lift weights or walk a lot in the first 3-4 days.

Possible complications and consequences of lumbar puncture:

irritation of the meninges;
persistent pain in the puncture area;
disc damage and hernia formation;
bleeding;
infection of the central nervous system.

More detailed information about the rules of the procedure and the cost of a needle for lumbar puncture can be obtained on the pages of our website Dobrobut.com.

Preparing for amniocentesis

To increase the effectiveness of the study and reduce the risks of possible complications, the patient should carry out the following preparatory measures:

Have a consultation with a doctor, where he will tell you in detail about the procedure, its possible complications, contraindications, etc.
Take tests and undergo an ultrasound to identify hidden infectious or inflammatory diseases, the presence of neoplasms, the volume of amniotic fluid, to confirm or refute a multiple pregnancy. They also help determine the gestational age, condition and viability of the fetus.
Approximately 4-5 days before amniocentesis, the patient should avoid taking acetylsalicylic acid or similar drugs, and 12-24 hours before, stop taking drugs that reduce blood clotting to reduce the risk of bleeding.

These measures must be performed in order to increase the safety of amniocentesis, reduce the risk of complications for the woman and her child, and increase the efficiency of diagnosis.

What to do after amniocentesis?

Since this procedure is invasive, there are a number of rules that a woman must follow to avoid possible complications:

It is necessary to exclude or, as far as possible, reduce any physical activity, especially heavy lifting.
Immediately after the procedure, ensure that you rest for several hours.
Patients with a negative Rh factor who are carrying a child with a positive Rh factor must undergo a course of injections of anti-Rhesus immunoglobulin for 72 hours. This is necessary in order to exclude Rh conflict due to the entry of amniotic fluid containing the genetic material of the fetus outside the amniotic sac.

Sometimes, to eliminate discomfort after amniocentesis, patients are prescribed painkillers. Also, in order to exclude inflammatory processes, non-steroidal anti-inflammatory drugs can be prescribed.

Indications for the study

The probability of giving birth to a defective child in a healthy pregnant woman is less than 3%. As a diagnostic method, amniocentesis provides a wealth of useful information, but is associated with some risks for the woman and fetus. Therefore, the study is not indicated for all pregnant women and is carried out under certain circumstances.

Direct indications for amniocentesis are the following factors:

High risk of chromosomal abnormalities based on biochemical screening or non-invasive test results;
In previous pregnancies there were chromosomal abnormalities in the fetus;
An ultrasound examination showed signs of various fetal developmental disorders;
There are genetic diseases in the family that are inherited;
Carriage of chromosomal rearrangements by one of the spouses.

Manipulations can be carried out in two ways:

The classic method is when a specialist inserts a puncture needle directly with his hand.
Using an adapter - an auxiliary device that ensures safe, accurate and efficient operation.

The procedure is carried out under ultrasound control. Most often it is performed without anesthesia. However, if the patient wishes, local anesthesia can be used.

After the procedure, the patient is under the supervision of a doctor in the ward for 2 hours. After this, if the woman feels normal, she goes home. For several days after the procedure, it is important to avoid physical activity, air travel, heavy lifting, sexual intercourse, and stress. If you experience pain in the lower abdomen, unusual vaginal discharge, or an increase in temperature, you should urgently consult a gynecologist.

When is amniocentesis performed?

This procedure can be performed at various stages of pregnancy, but not earlier than 10 weeks after conception. It is then that the formation of the main systems and organs of the fetus occurs, so amniocentesis will be effective as a diagnostic procedure. The optimal period for performing this operation is from 15 to 20 weeks. This is due to the fact that during this period the risk of damage to the fetus is significantly reduced, the volume of amniotic fluid increases, which makes it easier to take a sample for analysis.

The optimal period for amniocentesis is determined based on its goals:

to identify genetic disorders of the fetus, the puncture is performed at 15 weeks;
to check the formation of the respiratory system of the embryo, the optimal period is the 3rd trimester;
to determine the condition of the fetus in case of Rh conflict, amniocentesis is performed in the last months of pregnancy.

If for some medical reason (often these are fetal pathologies incompatible with life) a woman is prescribed an abortion, then through amniocentesis, injectable abortifacient drugs are injected into the bladder to terminate the pregnancy.

Material and methods

From June to December 2021, on the basis of the intensive care unit for infectious patients, we tested the technique of ultrasound guidance of lumbar puncture in children with disorders of the anatomy of the spine: most often scoliotic deformity due to organic damage to the central nervous system and cerebral palsy. In 16 patients (9 boys and 7 girls) aged from 3 to 10 years (5.5±2.31 years), with a body weight from 12 to 21 kg (15.4±2.84 kg) and aggravated premorbid background (organic damage to the central nervous system, spastic tetraparesis), a diagnostic lumbar puncture was planned. We used ultrasound to perform a preliminary scan of the spinal column to determine the best needle entry point.

After the patient was delivered to the manipulation room, standard gas induction of anesthesia with an oxygen-air mixture with sevoflurane (up to 8 vol%) was carried out and a laryngeal mask of the appropriate size was installed. Then the patient was placed on his side, with slight (maximum permissible) flexion in the lumbar spine. Maintenance of anesthesia: sevoflurane 3.5–4 vol%.

Using a GE LogiqBook ultrasound machine with a linear variable frequency sensor of 4–10 MHz, a preliminary scan of the spinal column at the lumbar level was performed.

As a starting point, we identified the sacrum by palpation and placed the sensor above it in the transverse plane (Fig. 1).

At the same time, the jagged structure of the bone with the underlying acoustic shadow was displayed on the screen. Then, gradually moving the sensor in a cranial direction, we marked the spinous processes of the L5, L4 and L3 vertebrae. On ultrasound, the spinous processes of the vertebrae look like small, sharp formations with bright hyperechoic edges, located directly under the skin. Typically, the L5 process is located slightly deeper than L4, but not always in the midline in patients with severe skeletal deformities. In any case, we marked the position of each spinous vertebra with a medical marker.

Next, by rotating the sensor 90° clockwise, we obtained a longitudinal image of the spine (Fig. 2). The semicircular transverse processes of the lumbar vertebrae with the underlying acoustic shadow, as well as the intervertebral spaces between them, are noticeable. In the first intervertebral space there is a bright, hyperechoic line of the ligamentum flavum with the underlying epidural space and the dura covering the conus of the spinal cord.

At the same time, the adjacent spinous processes were visible as bright, slightly caudally inclined, hyperechoic formations with a pronounced acoustic shadow. In the intervertebral space between them, nothing interferes with the propagation of the ultrasound beam, so it looks like an isoechoic gray strip between the dark anechoic shadows of the spinous processes. By moving the sensor higher or lower, we selected the widest intervertebral space (L4–L5 or L3–L4) in each patient. At the selected interval, we made a mark in the middle of the long axis of the sensor, obtaining a second point, from which we built a perpendicular to the line connecting the adjacent spinous processes at this level. Thus, we obtained the best point for passing the needle when performing a lumbar puncture.

Then, remaining in the same interspinous space, we returned the sensor to the transverse plane and slightly tilted it to achieve clear visualization of the dura mater (DRM). With this projection, the dural membrane looks like a bright, but thin, slightly rounded line that can fluctuate in time with the patient’s breathing. This phenomenon is especially noticeable in young children and with severe malnutrition. We measured the distance from the skin to the dura mater using the internal function of the ultrasound machine.

Thus, after a short ultrasound scan, we received data on the optimal point of needle insertion, the depth of the dura mater, and accurately identified the level of the procedure [6].

Then the ultrasound machine sensor was put aside and the traditional treatment of the procedure field and the doctor’s hands was carried out. Guided by the information obtained during preliminary scanning, we performed a lumbar puncture with a 25G Quincke needle according to the standard technique at a selected point with an inclination of 80–90° to the plane of the body surface.

The time of scanning and the time of the lumbar puncture procedure, the number of attempts and the number of needle redirections, the depth of needle insertion and the depth of the dura mater according to ultrasound, as well as the number and severity of complications of the procedure were noted. A complication was considered to be the appearance of blood in the needle pavilion or a large number of unchanged red blood cells in the resulting cerebrospinal fluid (more than 20 cells in the field of view).

The results obtained were processed using the statistical software package Statitica (for Microsoft Windows) using descriptive statistics methods for nonparametric data. We also compared the actual and ultrasound-predicted needle insertion depths using the Mann-Whitney U test.

Application of amniocentesis

Amniocentesis during pregnancy is used primarily as a diagnostic procedure to detect certain genetic disorders in the fetus - for example:

Down syndrome
, characterized by abnormalities in mental development, defects of internal organs and abnormal appearance;
Patau syndrome
, which is characterized by external abnormalities, developmental disorders of the central nervous system and brain, incompatible with life (the newborn dies a few days later);
Edwards syndrome
, accompanied by disturbances in the structure of internal organs (most often the heart), mental retardation, early mortality (the average life expectancy of such children is several months);
Turner syndrome
, which manifests itself exclusively in girls in the form of malformations of internal organs, infertility, short stature (although people with such pathology do not have deviations in intellectual development and can lead a full life);
Klinefelter syndrome
, characteristic only of men and accompanied by elongation of the limbs, high waist, gynecomatia, delayed puberty, testicular atrophy, infertility.

In addition to identifying genetic abnormalities in the fetus, amniocentesis during pregnancy is used to monitor the overall development of the child’s organs and systems in women at risk.

Indications for amniocentesis are:

The presence of genetic abnormalities in a pregnant woman or her relatives;
A woman’s age exceeds the 35-year mark (after which the risk of the formation of an extra 21 chromosome pair in the ovaries increases);
Results of an ultrasound examination - for example, identification of an enlarged gap between the neck bone and the skin of the fetus, characteristic of Down syndrome;
The results of biochemical screening are an excess of the normal level of hCG or an abnormally low concentration of PAPP-A (a specific protein contained in the blood plasma).

Another area of use of this technique is artificial termination of pregnancy. In this case, using a puncture needle, solutions of drugs that kill the fetus and promote its rejection and expulsion from the uterus are introduced into the amniotic fluid.

In what cases is lumbar puncture performed - indications for the study

A lumbar puncture, or spinal tap, is recommended when the doctor suspects a nervous system disorder, infection, or cancer.

The extracted liquid can be tested for compositional anomalies or the presence of diseases. Sometimes this is the only way to accurately determine the presence of infections of the nervous system.

There are a number of clinical cases where lumbar puncture is recommended more often than general diagnostic procedures:

Neonatal sepsis : This is a systemic blood infection in infants caused by a variety of diseases, including those affecting the nervous system - meningitis and encephalitis. If your doctor suspects that sepsis is caused by an infection of the nervous system, he will perform a lumbar puncture to determine the presence of pathogens in the cerebrospinal fluid.
Bacterial and viral infections : Germs can travel from the blood or lymph into the cerebrospinal fluid, where they can harm the body by affecting the nervous system. Congenital syphilis can also be diagnosed using a spinal tap.
Cancer detection : Cerebrospinal fluid may show the presence of cancer cells if the child has cancer that affects the blood, such as leukemia and lymphoma, or tumors of the nervous system or lymph nodes. High cerebrospinal fluid pressure in the nervous system can also help identify cell dysfunction and mass lesions.
Subarachnoid hemorrhage : This is bleeding in the subarachnoid space that damages the nervous system, including the brain. The presence of blood in the cerebrospinal fluid may indicate hemorrhage, which can occur due to a head injury or due to a ruptured aneurysm. An aneurysm is a weakness of the arterial walls that forms a pocket, like a balloon, that bursts and blood leaks into the surrounding tissue. An aneurysm can be caused by bacterial or viral infections, or congenital vascular defects.
Nervous system disorders : A puncture is a direct way of entering the nervous system to diagnose abnormalities or diseases. Neurodegenerative diseases, such as multiple sclerosis and Guillain-Barre syndrome, are detected through laboratory tests of cerebrospinal fluid, which can be obtained through a lumbar puncture.

There are other indications in which the doctor may perform a lumbar puncture to inject a substance rather than remove fluids:

Cerebrospinal fluid dye injection : A special dye is injected into the subarachnoid space to help the doctor see x-rays of the nervous system better. This allows the spinal cord and associated nerves to be properly examined and the results will be used to determine the disease.
Injectable chemotherapy drugs : Lumbar puncture is used to deliver chemotherapy drugs to the nervous system or even other parts of the body in case of cancer.
Injectable medications or anesthetics : Drugs may work faster if injected directly into the nervous system area through the cerebrospinal fluid.

Doctors may also use a lumbar puncture to administer drugs to the body if they feel it is the best way to administer the drug. In some cases, the doctor may insert a needle just to measure cerebrospinal fluid pressure, using a medical device called a manometer. High cerebrospinal fluid pressure is a critical indicator of certain diseases, such as meningitis.

Contraindications to amniocentesis

This diagnostic procedure is excluded if the patient has:

Elevated temperature;
Acute stage of chronic diseases;
Infectious diseases;
Factors that threaten the life of the fetus (placental abruption, uterine contractions);
Bloody discharge;
Congenital or acquired disorders of the structure of the uterus;
Infectious lesions of the abdominal cavity and its organs;
Low blood clotting; v
Benign neoplasms of the uterus (fibroids).

Contraindications

To reduce the risk of complications, there are contraindications in which the procedure is prohibited:

threat of placental abruption. This is a serious complication of pregnancy, which can result in the death of the woman or the unborn baby;
acute inflammatory processes or exacerbation of chronic pathologies. It does not matter where the inflammatory process develops. Even the active phase of ARVI is a contraindication for the procedure;
high body temperature;
benign and malignant tumors of the uterus;
anomalies of the anatomical structure of the uterus;
pathologies of the epidermis, dermis and subcutaneous fat layer in the area where the puncture will be made.

Complications during amniocentesis

Due to the invasive nature of this procedure, there are certain risks for the health of the child and the mother herself:

Spontaneous termination of pregnancy (miscarriage) or premature birth;
Violation of the integrity of the placenta or the tissues of the embryo itself with a puncture needle;
Damage to the bladder, uterus or other pelvic organs;
Inflammation of the amniotic sac, infection of the amniotic fluid with infectious agents;
Placental abruption, bleeding, damage to the umbilical cord, etc.

Even if amniocentesis is performed correctly, the patient may experience discomfort and pain in the abdominal area, bleeding, release of a small amount of amniotic fluid, etc.

Although in a medical setting the occurrence of these complications is minimized, the likelihood of them still remains. Therefore, doctors use this procedure relatively rarely, and when using it, they first warn the patient about the possible consequences. Often, alternative methods to amniocentesis are used to identify congenital defects in the fetus - for example, genetic analysis of embryonic DNA isolated from the woman’s blood plasma. Although this method shows less accurate results, it does not pose any threat to the life and health of the child.

The decision to perform amniocentesis is made by the pregnant woman herself after consultation with a specialist.
At her request, this procedure can be canceled or replaced with a safer or more effective one. However, amniocentesis remains one of the most effective ways to detect congenital abnormalities in the fetus, and therefore continues to be actively used in gynecological practice. To find out more, you can consult with our specialists by filling out the form: Make an appointment