Methods of prenatal diagnosis: genetic, invasive, non-invasive. Indications for appointment, results

2024 Author: Priscilla Miln | [email protected]. Last modified: 2023-12-16 00:21

Prenatal diagnosis is a complex examination of the development of pregnancy. The main goal is to identify various pathologies in an infant at the stages of intrauterine development.

The most common methods of prenatal diagnosis: ultrasound, the content of various markers in the blood of a pregnant woman, chorion biopsy, taking cord blood through the skin, amniocentesis.

Why prenatal diagnosis is needed

Using various methods of prenatal diagnosis, it is realistic to detect such disorders in the development of the fetus as Edwards syndrome, Down syndrome, disorders in the formation of the heart and other abnormalities. It is the results of prenatal diagnosis that can decide the future fate of the child. After receiving diagnostic data, together with the doctor, the mother decides whether the child will be born or the pregnancy will be terminated. Favorable prognosis may allow for rehabilitationfetus. Prenatal diagnosis also includes establishing paternity by genetic testing, which is carried out in the early stages of pregnancy, as well as determining the sex of the fetus. All these services in the capital are provided by the Center for Prenatal Diagnostics on Mira Avenue, headed by Professor M. V. Medvedev. Here you can undergo a comprehensive prenatal examination, including ultrasound. Modern technologies 3D, 4D are used in the Center.

Methods of prenatal diagnosis

Modern prenatal diagnostics uses a variety of methods and technologies. The degree, as well as the level of opportunities they have is diverse. In general, prenatal diagnosis is divided into two large groups: invasive prenatal diagnosis and non-invasive.

Non-invasive, or as they are also called, minimally invasive, methods do not involve surgical interventions and trauma to the fetus and mother. Such procedures are recommended for all pregnant women, they are not at all dangerous. Scheduled ultrasound examinations are a must. Invasive methods involve invasion (intervention) into the body of a pregnant woman, into the uterine cavity. The methods are not completely safe, so the doctor prescribes them in extreme cases, when there is a question about preserving the he alth of the unborn child.

Non-invasive prenatal diagnosis

Non-invasive methods include ultrasound or prenatal screening, which allows you to monitor the dynamics of the development of the fetus. Also considered non-invasiveprenatal diagnosis of the fetus by maternal serum factors.

Ultrasound is the most common procedure, has no harmful effects on the woman and the fetus itself. Should all mothers-to-be undergo this study? The question is debatable, maybe it is not required in every case. An ultrasound is prescribed by a doctor for many reasons. In the first trimester, you can determine the number of pregnancies, whether the fetus itself is alive, what is the exact period. At the fourth month, ultrasound can already show gross congenital malformations of the fetus, the location of the placenta, the amount of amniotic fluid. After 20 weeks, it is possible to determine the sex of the unborn child. It allows ultrasound to detect various anomalies if the analysis showed a high alpha-fetoprotein in the pregnant woman, and also if there are any malformations in the family history. It is worth noting that not a single ultrasound result can guarantee a 100% birth of a he althy fetus.

How an ultrasound is done

Prenatal antenatal ultrasound is recommended for all pregnant women at the following times:

• 11-13 weeks pregnant;
• 25-35 weeks pregnant.

Diagnosis of the state of the mother's body, as well as the development of the fetus, is provided. The doctor installs a transducer or sensor on the surface of the pregnant woman's abdomen, sound waves invade. These waves are captured by the sensor, and it transfers them to the monitor screen. In early pregnancy, the transvaginal method is sometimes used. In this case, the probe is inserted into the vagina. What abnormalities can be detected by ultrasound screening?

•Congenital malformations of the liver, kidneys, heart, intestines and others.

• Up to 12 weeks signs of development of Down syndrome.

Development of the pregnancy itself:

• Ectopic or uterine.

• Number of fetuses in the uterus.

• Pregnancy.

• Cerebral or breech presentation of the fetus.

• Timing delay.

• Heartbeat patterns. • Gender of the baby.

• Location and condition of the placenta.

• Blood flow in the vessels.

• Uterine tone.

So, ultrasound makes it possible to detect any deviations. For example, uterine hypertonicity can lead to a threatened miscarriage. Having discovered this anomaly, you can take timely measures to preserve the pregnancy.

Blood screening

Blood serum taken from a woman is examined for the content of various substances in it:

• AFP (alpha-fetoprotein).

• NE (unconjugated estriol).

• HCG (human chorionic gonadotropin). This method of prenatal screening has a fairly high degree of accuracy. But there are times when the test shows either a false positive or a false negative result. Then the doctor prescribes additional methods of prenatal screening, such as ultrasound or some kind of invasive diagnostic method.

The Center for Prenatal Diagnostics on Prospekt Mira in Moscow conducts biochemical screening, ultrasound, and prenatal consultation in just 1.5 hours. In addition to the first trimester screening, it is possible to undergo second trimester biochemical screening along with counseling and ultrasound.research.

Alpha-fetoprotein content

Prenatal diagnosis of hereditary diseases uses the method of determining the level of alpha-fetoprotein in the blood. This screening test allows you to identify the likelihood of a baby being born with a pathology such as anencephaly, spina bifida and others. Also, a high alpha-fetoprotein can indicate the development of several fetuses, incorrectly set dates, the possibility of miscarriage, and even a missed pregnancy. The analysis gives the most accurate results if it is done at the 16-18th week of pregnancy. Results before the 14th or after the 21st week are often erroneous. Sometimes blood donations are ordered. With a high rate, the doctor prescribes an ultrasound scan, this allows you to more reliably obtain confirmation of the disease of the fetus. If ultrasound does not determine the cause of the high content of alpha-fetoprotein, then amniocentesis is prescribed. This study more accurately determines the change in alpha-fetoprotein. If the level of alpha-fetoprotein in the patient's blood is increased, then complications during pregnancy may occur, for example, developmental delay, possible fetal death, or placental abruption. Low alpha-fetoprotein combined with high hCG and low estriol indicate the possibility of developing Down syndrome. The doctor takes into account all indicators: the age of the woman, the content of hormones. If required, additional prenatal research methods are assigned.

hcg

Human chorionic gonadotropin or (hCG) withearly pregnancy allows you to evaluate the most important indicators. The advantage of this analysis is the early timing of the determination, when even ultrasound is not informative. After fertilization of the egg, hCG begins to be produced already on day 6-8. HCG as a glycoprotein consists of alpha and beta subunits. Alpha is identical to pituitary hormones (FSH, TSH, LH); and beta is unique. That is why a test for the beta subunit (beta-hCG) is used to accurately obtain the result. In express diagnostics, test strips are used, where a less specific hCG test (urine) is used. In the blood, beta-hCG accurately diagnoses pregnancy as early as 2 weeks from fertilization. The concentration for the diagnosis of hCG in the urine matures 1-2 days later than in the blood. In urine, the level of hCG is 2 times less.

Factors affecting HCG

When determining hCG during early pregnancy, some factors that affect the result of the analysis should be taken into account.

Increased hCG during pregnancy:

• Discrepancy between the expected and real time.

• Multiple pregnancy (increase in result is proportional to the number of fetuses).

• Early toxicosis.

• Preeclampsia.

• Serious malformations.

• Reception of gestagens. • Diabetes mellitus.

Decrease in the level of hCG - a mismatch of the term, an extremely slow increase in the concentration of hCG by more than 50% of the norm:

• Mismatch between the expected and real terms (often due to an irregular cycle).

• Threatened miscarriage (more than 50% decrease).

• Miscarriage.

• Prematurity.

• Ectopic pregnancy.

•Chronic placental insufficiency.

• Fetal death in 2-3 trimester.

Invasive Methods

If the doctor decides that invasive prenatal diagnosis should be used to detect hereditary diseases, developmental disorders, one of the following procedures can be used:

• Cordocentesis.

• Chorionic biopsy (research the composition of the cells from which the placenta is formed).

• Amniocentesis (examination of amniotic fluid).• Placentocentesis (negative consequences after infections are detected).

The advantage of invasive methods is speed and a 100% guarantee of results. Used in early pregnancy. So, if there is any suspicion of abnormalities in the development of the fetus, prenatal diagnosis of hereditary diseases allows us to draw accurate conclusions. Parents and the doctor can decide in time whether to keep the fetus or terminate the pregnancy. If parents, despite the pathology, still decide to leave the child, doctors have time to properly manage and correct the pregnancy and even treat the fetus in the womb. If the decision to terminate the pregnancy is made, then in the early stages, when deviations are detected, this procedure is physically and mentally tolerated much easier.

Chorion biopsy

A chorion biopsy involves the analysis of a microscopic particle of the villous chorion - the cells of the future placenta. This particle is identical to the genes of the fetus, which allows us to characterize the chromosomal composition, determine genetic he althbaby. The analysis is carried out if there is a suspicion of diseases associated with chromosomal errors during conception (Edwards syndrome, Down syndrome, Patau, etc.) or at the risk of developing incurable diseases of cystic fibrosis, sickle cell anemia, and Huntington's chorea. The result of a chorion biopsy reveals 3800 diseases of the unborn child. But such a defect as a defect in the development of the neural tube cannot be detected by this method. This pathology is detected only during amniocentesis or cordocentesis procedures. At the time of the analysis, the thickness of the chorion should be at least 1 cm, this corresponds to 7-8 weeks of pregnancy. Recently, the procedure is carried out at the 10-12th week, it is safer for the fetus. But no later than the 13th week.

Carrying out the procedure

The puncture method (transcervical or transabdominal) is chosen by surgeons. It depends on where the chorion is located relative to the walls of the uterus. In any case, the biopsy is performed under ultrasound control.

The woman lies on her back. The selected puncture site is necessarily anesthetized with local exposure. The puncture of the abdominal wall, the walls of the myometrium is made in such a way that the needle enters parallel to the chorion membrane. An ultrasound monitors the movement of the needle. The syringe is used to take the tissues of the chorionic villi, the needle is removed. With the transcervical method, the woman is placed on a chair as in a normal examination. Explicitly expressed painful sensations are not felt. The cervix and the walls of the vagina are fixed with special forceps. Accessprovided with a catheter, when it reaches the chorionic tissue, a syringe is attached and material is taken for analysis.

Amniocentesis

Methods of prenatal diagnosis include the most common method for determining pathologies of fetal development - amniocentesis. It is recommended to carry it out at 15-17 weeks. During the procedure, the condition of the fetus is monitored by ultrasound. The doctor inserts a needle through the abdominal wall into the amniotic fluid, aspirates a certain amount for analysis, and the needle is removed. Results are being prepared in 1-3 weeks. Amniocentesis is not dangerous for the development of pregnancy. Fluid leakage may occur in 1-2% of women, and this will stop without treatment. Spontaneous abortion can occur only in 0.5% of cases. The needle does not damage the fetus, the procedure can be carried out even with multiple pregnancies.

Genetic methods

DOT-test is the latest safe genetic method in the study of the fetus, allows you to identify the syndrome of Patau, Edwards, Down, Shereshevsky-Turner, Klinefelter. The test is based on data obtained from the mother's blood. The principle is that with the natural death of a certain number of placental cells, 5% of the fetal DNA enters the mother's blood. This makes it possible to diagnose major trisomies (DOT test).

How is the procedure done? Blood is taken from the vein of a pregnant woman, fetal DNA is isolated. The result is issued within ten days. The test is carried out at any stage of pregnancy, starting from the 10th week. Reliability of information 99.7%.