Methods of prenatal diagnosis: genetic, invasive, non-invasive
Prenatal diagnosis is a complex of examinations of pregnancy development. The main goal is the detection of various pathologies in the infant at the stages of intrauterine development.
The most common methods of prenatal diagnosis: carrying out ultrasound, the content of various markers in the blood in a pregnant woman, a biopsy of the chorion, taking through the cord blood cord, amniocentesis.
Why Prenatal Diagnosis is Needed
Applying various methods of prenatal diagnosis, it is really possible to detect in the development of the fetus such disorders as Edwards syndrome, Down's syndrome, disorders in heart formation and other abnormalities. Precisely the results of prenatal diagnosis can decide the fate of the child. After receiving the diagnostic data in conjunction with the doctor, the mother decides whether the child will be born or the pregnancy will be interrupted. Favorable predictions may allow for the rehabilitation of the fetus. The prenatal diagnosis includes the establishment of paternity by the method of genetic examination, which is carried out in the early stages of pregnancy, as well as the determination of 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. Used in the Center of modern technology 3D, 4D.
Methods of prenatal diagnosis
Modern prenatal diagnostics employs a wide variety of methods and technologies. Degree, as well as the level of opportunities they have varied. 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 provide for surgical interventions and trauma to the fetus and mother. Such procedures are recommended for all pregnant women, they are not at all dangerous. Scheduled examinations of ultrasound must necessarily pass. Invasive methods involve the invasion (intervention) in the body of a pregnant woman, into the uterine cavity. The methods are not completely safe, so the doctor appoints them in extreme cases, when there is a question about preserving the health of the unborn child.
Noninvasive prenatal diagnosis
Non-invasive methods include ultrasound or prenatal screening, which allows you to observe the dynamics behind the development of the fetus. Non-invasive is also considered prenatal diagnosis of the fetus according to the serum factors of the mother's blood.
Ultrasound is the most common procedure, it has no harmful effects on a woman and the fetus itself. Do all future mothers have to undergo this research? The question is controversial, maybe it is not required in every case. Ultrasound is prescribed by the 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 time. In 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. Allows ultrasound to detect various anomalies if the analysis showed a pregnant woman a high alpha-fetoprotein, and if a family history has some developmental defects. It is worth noting that no result of ultrasound can guarantee 100% birth of a healthy fetus.
How is ultrasound performed?
Prenatal antenatal diagnosis in the form of ultrasound is recommended for all pregnant women on the following terms:
- 11-13 week of pregnancy;
- 25-35 week of pregnancy.
There is a diagnosis of the state of the mother's body, as well as the development of the fetus. The transducer or sensor the doctor places on the surface of the abdomen of a pregnant woman, an invasion of sound waves occurs. These waves are picked up by the sensor, and it transfers them to the monitor screen. In the early stages of pregnancy, the transvaginal route is sometimes used. In this case, the sensor is inserted into the vagina. What abnormalities can reveal the screening of ultrasound?
• Congenital malformations of the liver, kidneys, heart, intestines and others.
• Up to 12 weeks of development of Down syndrome.
The development of pregnancy itself:
• Ectopic or uterine.
• The number of fetuses in the uterus.
• Gestational age.
• Head or pelvic presentation of the fetus.
• Lagging in development by maturity.
• The nature of the heartbeat.
• The sex of the child.
• The location and condition of the placenta.
• Blood flow in the vessels.
• Tonus of the uterus.
So, ultrasound examination makes it possible to detect any deviations. For example, hypertension of the uterus can lead to a threat of miscarriage. Having found out this anomaly, it is possible to take measures in time on preservation of pregnancy.
Screening by blood
The blood serum taken from a woman is examined for the content of various substances in her:
• AFP (alpha-fetoprotein).
• NE (unconjugated estriol).
• HG (chorionic gonadotropin).
This method of prenatal screening has a fairly high degree of accuracy. But there are cases when the test shows either false-positive or false-negative results. Then the doctor prescribes additional methods of prenatal screening, such as ultrasound or some method of invasive diagnosis.
The center for prenatal diagnostics on Mira Avenue in Moscow spends just 1.5 hours biochemical screening, ultrasound, and also gives a prenatal consultation. In addition to screening the first trimester, it is possible to undergo biochemical screening for the second trimester, along with counseling and ultrasound.
The content of alpha-fetoprotein
Prenatal diagnosis of hereditary diseases uses the method of determining the level of alpha-fetoprotein in the blood. This screening test can reveal the probability of the birth of a baby with a pathology such as anencephaly, spina bifida and others. Also, a high index of alpha-fetoprotein may indicate the development of several fetuses, in abnormal terms, the possibility of miscarriage and even a frozen pregnancy. The most accurate results are given if done at the 16-18th week of pregnancy. Results before the 14th or after the 21st week are often erroneous. Sometimes a re-surrender of blood is prescribed. At a high rate, the doctor prescribes ultrasound, this allows more reliable confirmation of the disease of the fetus. If ultrasound does not determine the cause of a 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 is increased in the patient's blood, complications may occur during pregnancy, for example, delay in development, possibly fetal death, or placental abruption. Low alpha-fetoprotein combined with high CG and low estriol indicate the possibility of Down's syndrome. The doctor takes into account all the indicators: the age of the woman, the content of hormones. If necessary, additional prenatal testing methods are prescribed.
Human chorionic gonadotropin or (hCG) in early pregnancy allows you to assess the most important indicators. Plus this analysis - the early terms of the definition, when even ultrasound is not informative. After fertilization of the ovum, HCG is already produced on day 6-8.
HCG as a glycoprotein consists of alpha and beta subunits. Alpha is identical with the pituitary hormones (FSH, TTG, LH); and beta is unique. This is why a beta-subunit test (beta-hCG) is used to obtain an accurate result. In express diagnostics, test strips are used, where a specific HCG test (for urine) is not used. In the blood beta-hCG accurately diagnoses pregnancy as early as 2 weeks from fertilization. Concentration for the diagnosis of hCG in the urine ripens 1-2 days later than in the blood. In urine the level of hCG is 2 times less.
Factors affecting hCG
Determining hCG during pregnancy in the early stages, it is necessary to consider some factors that affect the result of the analysis.
Increase in hCG during pregnancy:
• Inconsistency between the estimated and real time.
• Multiple pregnancy (the increase in the result is proportional to the number of fruits).
• Early toxicosis.
• Serious malformations.
• Gestagen administration.
Lowering the level of hCG - inconsistency, extremely delayed increase in HCG concentration more than 50% of the norm:
• Inconsistency between the intended and real term (mostly due to an irregular cycle).
• Threat of miscarriage (the level decreases by more than 50%).
• Frozen pregnancy.
• Ectopic pregnancy.
• Chronic placental insufficiency.
• Fetal death in the 2-3 trimester.
If the doctor decides that invasive prenatal diagnosis should be used to identify hereditary diseases, developmental disorders, one of the following procedures may be used:
• Chorion biopsy (study of the composition of cells from which the placenta is formed).
• Amniocentesis (study of amniotic fluid).
• Placentocentesis (negative consequences after the transferred infections are revealed).
The advantage of invasive methods is the speed and absolute guarantee of the result. Used in early pregnancy. So, if there are any suspicions of abnormalities in the development of the fetus, prenatal diagnosis of hereditary diseases makes it possible to draw accurate conclusions. Parents and the doctor can decide in time: to leave the fetus or to terminate the pregnancy. If the parents, despite the pathology, still decide to leave the child, the doctors have time to properly manage and adjust the pregnancy and even treat the fetus in the womb. If the decision on termination of pregnancy is accepted, then in the early stages, when the deviations are detected, physically and morally this procedure is much easier to transfer.
A chorionic biopsy involves the analysis of a microscopic particle of a villous chorion, a cell of the future placenta. This particle is identical to the fetal genes, which makes it possible to characterize the chromosome composition, to determine the genetic health of the baby. The analysis is performed with suspicion of diseases associated with chromosomal errors during conception (Edwards syndrome, Down's syndrome, Patau, etc.) or at the risk of developing incurable diseases of cystic fibrosis, sickle cell anemia, Gentygton's chorea. The result of a chorion biopsy allows to reveal 3800 diseases of the future child. But such a defect as a defect in the development of the neural tube can not be detected by this method. This pathology is found only in the procedures of amniocentesis or cordocentesis.
At the time of the analysis, the thickness of the chorion should be at least 1 cm, which corresponds to 7-8 weeks of pregnancy. Recently, the procedure is carried out at the 10-12th week, it is more safe for the fetus. But not later than the 13th week.
The method of puncture (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, a biopsy is performed with ultrasound.
The woman is lying on her back. The chosen place for a puncture is necessarily anesthetized by local influence. The puncture of the abdominal wall, the wall of the myometrium, is performed in such a way that the needle enters parallel to the chorion membrane. The movement of the needle is controlled by ultrasound. A syringe is sampling the tissues of the chorion villi, the needle is removed. In the transcervical mode, the woman is placed on the chair as in a normal examination. Clearly expressed painful sensations are not felt. The cervix and the walls of the vagina are fixed with special forceps. Access is provided by a catheter, when the chorionic tissue reaches it, a syringe is attached and the material for analysis is taken.
Methods of prenatal diagnosis include the most common method of determining pathologies of fetal development - amniocentesis. It is recommended to hold it at 15-17 weeks. During the procedure, the condition of the fetus is controlled by ultrasound. The doctor through the abdominal wall introduces the needle into the amniotic fluid, sucks some quantity for analysis and the needle is removed. Prepared results 1-3 weeks. Amniocentesis is not dangerous for the development of pregnancy. 1-2% of women may have fluid leakage, this ceases without treatment. Spontaneous abortion can occur only in 0.5% of cases. The fetus does not damage the fetus, it is possible to carry out the procedure even with multiple pregnancies.
The DOT test is the newest safe genetic method for the study of the fetus, it allows to identify the syndrome of Patau, Edwards, Down, Shereshevsky-Turner, Klinefelter. The test is based on data that is obtained from the mother's blood. The principle is that with the natural death of a number of cells of the placenta falls into the mother's blood 5% of the fetal DNA. This makes it possible to diagnose the main trisomy (DOT test).
How is the procedure performed? The blood from the vein of a pregnant woman is taken, the fetal DNA is allocated. The result is given within ten days. The test is carried out at any time of pregnancy, starting from 10 weeks. Reliability of information is 99.7%.