Invasive methods of prenatal diagnosis

Invasive methods of prenatal diagnosis are widely used to identify a large number of fetal diseases, including genetic diseases and chromosomal abnormalities (trisomy of 18 and 21 pairs of chromosomes, catnip scream, Duchenne muscular dystrophy, neural tube defects, congenital metabolic disorders, etc. .), as well as the detection of violations of the fetus.

[1], [2]

Amniocentesis

Collection of amniotic fluid for biochemical, hormonal, immunological, cytological and genetic studies, allowing to judge the condition of the fetus. Indications for amniocentesis are: isoserological incompatibility of blood of the mother and fetus, chronic hypoxia of the fetus (pregnancy repetition, OPG gestosis, extragenital diseases of the mother, etc.), establishment of the degree of maturity of the fetus, antenatal sex diagnosis, cardiological examination for fetal malformations, microbiological study.

Depending on the site of the puncture, transvaginal and transabdominal amniocentesis are distinguished. Transvaginal amniocentesis is recommended to be performed at term of pregnancy up to 16-20 weeks, transabdominal - after 20 weeks. The operation is always performed under ultrasound control, choosing the most convenient puncture site, depending on the location of the placenta and small parts of the fetus.

With transabdominal amniocentesis after treatment of the anterior abdominal wall with an antiseptic solution, anesthesia of the skin, subcutaneous tissue and subaponeurotic space with a 0.5% solution of novocaine is performed. For the study, at least 40 ml of amniotic fluid is needed. Place the puncture on the anterior abdominal wall treated with an antiseptic and apply an aseptic sticker. Transvaginal amniocentesis is performed through the anterior fornix of the vagina, the cervical canal or the posterior vaginal vault. The choice of the location of the puncture needle depends on the location of the placenta. After preliminary sanitation of the vagina, the cervix is fixed with bullet forceps, shifted up or down, depending on the method chosen, and a puncture of the vaginal wall is made at an angle to the wall of the uterus. When the needle penetrates into the uterine cavity, amniotic fluid is released from its opening.

The biochemical composition of amniotic fluid is relatively constant. There are slight fluctuations in the concentration of mineral and organic substances, depending on the period of pregnancy and the state of the fetus. The pH of amniotic fluid correlates with that of fetal blood obtained from the skin of the fetal head. At full term pregnancy, the pH of amniotic fluid is 6.98-7.23. The most informative for the diagnosis of fetal hypoxia is the pH value (less than 7.02), pCO2 (over 7.33 kPa), p02 (less than 10.66 kPa), potassium concentration (over 5.5 mmol / l), urea (7 , 5 mmol / L) and chlorides (higher PO mmol / L). One of the important indicators of metabolism in amniotic fluid is creatinine, the concentration of which increases with the progression of pregnancy and at the end it is 0.18-0.28 mmol / l. Creatinine reflects the degree of maturity of the kidneys of the fetus, an increase in its level in the amniotic fluid is observed with fetal hypotrophy and late toxicosis of pregnant women. An increase in protein content in amniotic fluid may indicate hemolytic disease, intrauterine fetal death, anencephaly and other fetal development abnormalities. The level of glucose in the amniotic fluid of 15 mg / 100 ml and above 'is a sign of the maturity of the fetus, below 5 mg / 100 ml - its immaturity. When pregnancy is overdrawn, the concentration of glucose decreases by 40% due to a reduction in glycogen content in the placenta due to dystrophic changes.

To determine the hemolytic disease of the fetus, determine the optical density of bilirubin (CBP) in the amniotic fluid. The value of the OPB is established using a spectrophotometer at 450 nm. When the OPB is below 0.1, the spectrophotometric curve is evaluated as physiological.

[3], [4], [5], [6],

Cytological study of amniotic fluid

To diagnose the degree of maturity of the fetus, cytological examination of the amniotic fluid is carried out. The main source of the cellular composition of the amniotic fluid is the skin and the epithelium of the fetal urinary tract. Its composition includes the epithelium of the amnion, the umbilical cord and the mouth cavity of the fetus. To obtain and investigate the precipitate, the amniotic fluid is centrifuged at 3000 rpm for 5 minutes, the smears are fixed with a mixture of ether and alcohol, then stained using the method of Garras-Shore, Papanicolaou, or 0.1% Nil sulphate solution, which stains the non-nuclear lipid-containing cells product of the sebaceous glands of the fetal skin) in orange (the so-called orange cells). The percentage of orange cells in the smear corresponds to the maturity of the fetus: up to 38 weeks of pregnancy, their number does not exceed 10%, over 38 weeks - up to 50%. To assess the maturity of the fetal lungs, the concentration of phospholipids in the amniotic fluid is measured, especially the lecithin / sphingomyelin ratio (L / C). Lecithin, saturated phosphatidylcholine, is the main active ingredient in surfactant. The values of the ratio M / C are interpreted as follows:

• L / C = 2: 1 or more - light mature; Only 2% of cases of newborns are at risk of developing respiratory distress syndrome;
• L / C = 1,5-1,9: 1 - the probability of developing respiratory distress syndrome is 50%;
• L / C = less than 1.5: 1 - in 73% of cases, development of respiratory distress syndrome is possible.

In everyday practice, use a qualitative assessment of the ratio of lecithin and sphingomyelin (foam test). To this end, 3 ml of ethyl alcohol are added to a test tube containing 1 ml of amniotic fluid and the tube is shaken for 3 minutes. The resulting ring of foam indicates the maturity of the fetus (positive test), the absence of foam (negative test) indicates the immaturity of the lung tissue.

The study of amniotic fluid for the purpose of diagnosis of congenital malformations is usually performed at the gestational age of 14-16 weeks. Fetal cells contained in the amniotic fluid and used for genetic studies are grown on tissue culture. Indications for amniocentesis in this case are:

• the age of a woman older than 35 years (given the high risk of forming trisomy for 21 pairs of chromosomes);
• Availability. Chromosomal diseases in children born earlier;
• Suspicion of diseases linked to the X chromosome in the mother.

Complications of amniocentesis: premature discharge of amniotic fluid (more often with transcervical access), wound of fetal vessels, wound of the bladder and intestines of the mother, chorionamnionitis; less - premature birth, placental abruption, fetal injury and umbilical cord injury. However, due to the wide introduction of ultrasound control, complications of amniocentesis are extremely rare.

[7], [8], [9], [10], [11], [12],

Chorionic villus biopsy

An operation whose purpose is to obtain cells of the villous chorion for karyotyping the fetus and determining chromosomal and gene anomalies (including the determination of hereditarily caused metabolic disorders). Sampling is carried out transcervical or transabdominal in the period from 8 to 12 weeks of pregnancy under the supervision of ultrasound scanning. Complications of chorionic villus biopsy may include intrauterine infection, bleeding, spontaneous abortions, hematomas. More recent complications include premature birth, low birth weight (<2500 g), malformations of the fetus. Perinatal mortality reaches 0.2-0.9%.

[13], [14], [15]

Cordocentesis

Cordocentesis (obtaining fetal blood samples by puncturing the umbilical cord) is performed for fetal karyotyping and immunological studies. Relative contraindications for cordocentesis are low blood pressure, polyhydramnios, unsuccessful location of the fetus. Potential complications (1-2%): chorionamnionitis, outpouring of amniotic fluid, rhesus immunization, fetal bleeding, umbilical cord hematoma, intrauterine growth retardation.

[16], [17], [18], [19],

Fetal surgery

With the improvement of the methods of ultrasound and invasive prenatal diagnostics, the opportunity has opened up for the development of a new direction in perinatology - fetal surgery. Some pathological conditions of the fetus can be corrected before birth, which prevents the birth of children in a serious condition. The first intrauterine surgical operation - replacement fetal blood transfusion - was performed in severe form of hemolytic disease of the fetus by means of cordocentesis. However, the high incidence of intrauterine fetal death does not allow widespread use of this method.

Another direction of fetal surgery is associated with the puncture and emptying of pathological fluid accumulations in the fetal cavities (hydrothorax, ascites, hydropericardium) arising in cases of immune and nonimmune fetal dropsy.

Attempts have also been made in intrauterine treatment of the fetus with hydrocephalus, which was reduced to the implantation of a ventriculo-amniotic shunt to reduce intracranial pressure. Despite encouraging results of experimental studies, the value of clinical application of the method has not been finally established: perinatal mortality among treated fetuses was 18%; 66% of the survivors had physical and mental development disorders from moderate to severe.

Promising are operational aids in reverse arterial perfusion in twins (specific pathology in multiple pregnancies, characterized by vascular messages between the fruits that can be the cause of death of one or the other twin). Reverse arterial perfusion occurs only in twins with fused placentas. With congestive heart failure (the appearance of pericardial effusion), a puncture of the hydropericardium is performed; with polyhydramnios - therapeutic amniocentesis. In addition, ligation of the communicating vessels in the umbilical cord or their laser coagulation performed under endoscopic control is possible.

[20], [21], [22], [23]