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Genetic diseases (prenatal diagnosis)
Close concepts: antenatal diagnosis of genetic diseases, genetic diagnosis at the person
Not only obstetricians-gynecologists and pediatricians, but also all doctors whom the patients who are in reproductive age see have to be familiar with prenatal diagnosis of genetic diseases. The family doctors well familiar with the anamnesis of a family and interested in that in a family anomaly did not appear, have to undertake part of responsibility for genetic consultation. Only the highly skilled doctor geneticist can resolve some difficult questions of genetic consultation, however the trained expert doctor can quite solve many ordinary problems. The modern diagnostic equipment allows to find vnutriutrobno practically all chromosomal diseases, many is monogenic the inherited diseases and some poligenno (mnogofaktorialno the inherited diseases).
In order that it is correct to hold consultation, the doctor has to:
1) to collect the full family anamnesis;
2) to be able to understand the main mechanisms of inheritance;
3) to precisely know a technique of diagnosis of the suspected pathology;
4) to represent potential influence of factors of environment on the developing fruit;
5) to know possibilities of modern diagnosis.
Spouses have to be precisely informed on degree of genetic risk for a fruit and on the forecast for the child having disturbances about which there is a speech. In ideal conditions spouses should discuss with the doctor potential risk of the birth of the child with congenital anomaly even before conception or in the first 3 months of pregnancy. They have to be informed on opportunities of prenatal diagnosis and on potential complications of an amniotsentez. Bleeding, infection and a sensitization with group antigens of blood can be complication for mother. Complication for a fruit is the abortion and an injury of a fruit. (In detail these complications are discussed below). It is necessary to warn spouses that procedure of the analysis takes 3 — 5 weeks.
Technique of an amniotsentez
Genetic amniotsentez the doctor-obstetrician having the experience of carrying out this manipulation and capable to cope with possible complications will see off. The personnel of laboratory have to have the fulfilled technique of cultivation and the analysis of cells of amniotic liquid. Amniotsentez carry usually out on an outpatient basis. It is the best of all to carry out it on 15 — the 16th week of pregnancy when its interruption in case of need is still possible. To this term the uterus is easily palpated also amniotic liquid enough safely to carry out amniotsentez.
Before amniotsentezy it is necessary to execute ultrasonic research of a uterus in order that:
1) to establish viability of a fruit;
2) to confirm duration of gestation;
3) to diagnose a possible multiple pregnancy;
4) to establish a placenta arrangement;
5) to find the expressed anomalies of a fruit or a gidatida of a uterine tube;
6) to find possible anomalies of a uterus and appendages;
7) to reduce in the future probability of a potential sensitization of mother group antigens of a fruit.
Before amniotsentezy the woman has to urinate. Manipulation is carried out in the conditions of a strict asepsis. The place of a puncture is infiltrirut by 1% lidocaine solution. The one-time spinal needle with a stylet (length of 9 cm, caliber 22 or 20) is entered through skin into a bag of waters. Then the stylet is deleted and carry out trial aspiration by the syringe to avoid pollution by mother cells. If the first several milliliters of liquid are painted by blood, aspirate them, and then attach other syringe until pure liquid begins to arrive. In the second or third syringe gain 20 — 30 ml of amniotic liquid and send to laboratory in the same syringe or in sterile plastic (or glass, but covered with silicone) to a test tube. It is important to inscribe correctly test and to transport it at the room temperature. It is desirable that in laboratory test was immediately processed as storage or long transportation of tests lead to decrease in accuracy of the analysis. After an amniotsentez the patient some time is watched, and then allow to go home, having instructed that she avoided at least several days of exercise stresses. At emergence of allocations or bleedings from a genital tract, pains or fever, it is necessary to see a doctor immediately. And at last, all fruits in case of an abortion and all newborns have to look round for the purpose of detection of hereditary pathology.
By outward urine and amniotic liquid cannot be distinguished, besides, the analysis of mother cells instead of cells of a fruit can lead to the wrong diagnosis. Similar mistakes arise at aspiration of urine of mother instead of amniotic liquid as amniotsentez carry usually out in suprapubic area.
Authors found out that when drying amniotic liquid on the glass processed by acid at small increase (X100) the characteristic treelike picture of crystallization is defined. This method can be used for fast differentiation of amniotic liquid from urine with a fine precision.
It is clinically possible to suspect a multiple pregnancy of cases when the uterus size more assumed on the term of the last periods, however, this representation happens wrong, especially at corpulent women. Before amniotsentezy it is necessary to exclude a multiple pregnancy by means of ultrasonic research. In cases of a multiple pregnancy the independent puncture of each bag of waters is necessary for definition of a condition of each fruit. In the presence of two fruits after the first puncture and aspiration it is possible to enter dye, for example indigo carmine into a bag of waters, and to carry out a puncture of the second bubble under control of an ekhografiya. If at the second puncture transparent liquid is received, means successfully punktirovan the second bubble if painted — the first. By means of this method authors managed to obtain genetic information, separate for each of twins, approximately in 90% of the studied cases. The impression is made that repeated punctures in cases of a multiple pregnancy do not represent additional risk neither for mother, nor for fruits in comparison with a single puncture. And at last, at a multiple pregnancy one fruit can be normal, and another — with pathology. It is necessary to prepare parents for this situation.
As there is always a theoretical risk a Rhesus factor sensitization, authors recommend to appoint to Rh-negative women anti-D - immunoglobulin if they amniotsentez see off at the term of 6 months of pregnancy and later.
Possible complications of an amniotsentez
Amniotsentez with crops of cells of amniotic liquid — rather safe and very exact (more than 99%) research. Nevertheless any surgical manipulation is not deprived completely risk.
Therefore use of an amniotsentez at prenatal diagnosis is limited to cases in which need to precisely establish the diagnosis prevails over risk of potential complications.
Speaking about probable complications of an amniodentez, it is reasonable to consider separately risk for an organism of mother and for a fruit organism. The abortion, an injury with a needle, an infection and possible effects of removal of a certain amount of amniotic liquid and disturbance of an integrity of an amniotic cover can threaten a fruit (for example, contractures of joints or amniotic commissure). Kagr and Hayden found traces of small injuries of skin (deepenings and linear hems) approximately in 3% of children whose mothers transferred amniotsentez on 5 — the 6th month of pregnancy. However, the probability of serious complications at a fruit is very small (less than 1:1000 research.
In several cooperative researches tried to estimate risk of an amniotsentez precisely. The first prospective research was organized by National institute of health of the child and development of the person of the USA and included 1040 investigated and 992 control sampling units. According to the obtained data, the frequency of immediate complications (bleeding, the expiration of amniotic liquid and an abortion) made about 2% that only slightly exceeded probability of the spontaneous complications of pregnancy observed in control group. Moreover, only the few from the specified complications were rather serious. In the sum among the women who underwent an amniotsentez, the frequency of an abortion made 3,5%, and in control group on the same durations of gestation — 3,2%. The impression was made that with increase in number of attempts of an amniotsentez the probability of the subsequent abortion increases. Only one case of death of a fruit owing to a puncture was established. In this research cases of the amnionitis caused amniotsentezy were not registered. Researchers from Canada received similar results. But cooperative research in Great Britain found authentically higher frequency of an abortion after an amniotsentez (2,6%) in comparison with control group (1,1%), and also the inexplicable higher frequency of a syndrome of respiratory insufficiency in newborns of the studied group. However, this work is not deprived of some tendentiousness as women of control group were authentically more senior and among them was more multipara.
If to take into account distinctions in the organization and the protocol of the given researches, then the difference in their results will become insignificant. So, it is possible to draw the following conclusions:
1. Increase of risk of an abortion owing to an amniotsentez makes about 0,5%;
2. The risk of a serious injury of a fruit is insignificant.
3. The risk of harmless scratches of a fruit a needle is small.
4. The risk of complications at mother minimum, the only real complication is represented an amnionitis which probability is small.