Double and threefold tests
Prenatal (dorodovy) screening (or “selection, sifting“) are safe for future mother and her child of research which is conducted by everything to pregnant women to reveal risk group of a number of complications of pregnancy.
One of options of prenatal screening is calculation of risk of congenital pathology of a fruit, Now this examination is conducted by everything to pregnant women in I and II trimesters,About what pathology there is a speech
Prenatal screening allows to estimate risk of presence at the child of chromosomal pathology (a Down syndrome and Edwards`s syndrome) and defects of a zarashcheniye of a neural tube.
the Down syndrome - one of widespread chromosomal pathologies at which emergence of an additional chromosome in 21 - y to couple is observed (a trisomiya 21). Such children have a characteristic phenotype (appearance), a delay of intellectual development and a set of anomalies from internals and fabrics.multiple malformations including psychomotor are also characteristic
Of Edwards`s syndrome (a trisomiya 18). As a rule, such children are impractical. This disease meets less than a Down syndrome.
the Defects of a Zarashcheniye of a Neural Tube (DZNT) are a lack of a brain (anentsefaliya) and a nezarashcheniye of the spinal channel (spina bifida).What biochemical markers define
several types of prenatal screening Exist. One of them is biochemical screening, i.e. determination of concentration of some substances in blood of the pregnant woman. For this purpose future mother needs to take a blood test from a vein, it is desirable on an empty stomach.by
during research estimates the level of a free subjedinitsa of b - HGCh and the plasma protein associated with pregnancy (RARR - And) in the I trimester of pregnancy and a free estriol (E3), an alpha - a fetoprotein (AFP) and b - HGCh in the II trimester. The choice of these markers is not casual. The matter is that out of pregnancy these substances or are absent in the woman`s blood, or contain in very insignificant quantity. And education them happens in cages of a fruit or a placenta from where then they get to mother`s blood-groove where their level changes depending on a condition of a fruit and term of pregnancy. Emergence of any pathology finds the reflection in a deviation of these markers from norm.
b - HGP (horionichesky gonadotrophin of the person) - the specific hormone of pregnancy necessary for its preservation. From the first days after conception it is synthesized by cages of one of covers of fetal egg (horion), in the subsequent it proceeds in placenta cages. Normal between 2 - y and 5 - y for weeks of pregnancy concentration of hormone doubles each 1,5 days, reaching peak on 10 - 11 - y to week, and then decreases. Only on 33 - 35 - y weeks of pregnancy again small increase of level b - HGCh is noted, the Increase in content of hormone in blood considerably exceeding norm is observed at a Down syndrome, and decrease allows to suspect Edwards`s syndrome.However the greatest diagnostic value this marker has
in the II trimester of pregnancy, and in the I trimester of more informative the assessment of a free subjedinitsa of b - HGCh is. In the presence of chromosomal pathology of change of concentration are similar to that at - HGCh: the Down syndrome is followed by increase, and Edwards`s syndrome - reduction of level of a free subjedinitsa.
One more indicator defined on early terms of pregnancy is the plasma protein associated with pregnancy - And (RARR - And). He participates in the biochemical reactions influencing growth and development of a fruit, growth and functioning of a placenta and also participates in the immune answer of an organism of mother. In a large number of RARR - And it is developed by cages of a fetal cover (trofoblast). With increase in term of pregnancy also the RARR level - And grows in the woman`s blood. At a Down syndrome and Edwards`s syndrome there is a reduction of its concentration.by
In the II trimester along with b - HGCh is estimated the level of one more hormone - a free estriol (the main estrogen of pregnancy) produced by a placenta, the substances produced by adrenal glands and passing transformation in a fruit liver are necessary For its synthesis. Its main function - ensuring growth of a uterus and preparation of mammary glands for a lactation. Normal, since the moment of formation of a placenta, the level of a free estriol progressively increases. First of all it reflects a condition of a fetoplatsentarny complex which included a uterus wall, a placenta and vessels of an umbilical cord. Sharp decrease in content of hormone is possible at fetoplatsentarny insufficiency, nadpochechnikovy insufficiency at a fruit, at a Down syndrome and Edwards`s syndrome, an anentsefaliya and other defects of the central nervous system.
the Last biochemical marker entering screening researches - an alpha - fetoprotein (AFP). It is one of the main proteins of plasma of a fruit. In the beginning it is synthesized in a zheltochny bag (one of fetal covers), and then - in a liver and zheludochno - an intestinal path of a fruit. Growth of the contents of AFP in blood of the pregnant woman is observed after 10 - y weeks. To 30 - y to week its concentration reaches a maximum and then decreases, Change of this indicator allows to suspect defect of a zarashcheniye of a neural tube as in such situation there is considerable exit an alpha - a fetoproteina in amniotic liquid (amniotic waters) from where it is soaked up in a maternal blood-groove. I.e. increase in concentration of AFP in blood of the pregnant woman is observed. There are also other hereditary anomalies of development of a fruit which are followed by growth of level an alpha - a fetoproteina. And decrease in AFP is characteristic of a Down syndrome and Edwards`s syndrome.
By quantity of the estimated biochemical indicators prenatal screening of the I trimester differently is called “the double test“, and the II trimester - “the threefold test“.
If you got to risk groupIt is necessary to understand that the probability of detection of pathology and development of this pathology is not same. Detection of the increased risk of emergence of any deviations from the normal course of pregnancy or normal development of a fruit is not the diagnosis at all. To the pregnant women who got to risk group the special additional researches allowing to confirm or exclude existence of pathology are surely conducted.
When carry out researches?prenatal screening is recommended to be carried out by
In the I trimester on 10 - 14 - y to week of pregnancy (optimum - on 11 - 13 - y to week). Inspection can be passed in the II trimester with 14 - y on 20 - yu week (optimum - on 16 - 18 - y to week).Time of carrying out screening researches is also chosen by
not casually. At the same time the complex of factors is considered. In - the first, it is the maximum informational content of indicators, in - the second, the pregnancy term on which carrying out additional researches will be the safest for the woman and the child.
Simultaneous use of one more simple and available method - ultrasonic research - helps to increase the accuracy and reliability of prenatal diagnostics. Screening provides carrying out BONDS - researches in the I trimester of pregnancy (on 11 - 13 - y to week). During this period the quantity of fruits in a uterus iy viability is defined, pregnancy term is specified (on a tailbone - to the parietal size - KTR), rough malformations are excluded and markers of chromosomal pathology of a fruit (thickness of vorotnikovy space, existence or lack of a nasal bone) are defined. At the term “thickness of vorotnikovy space“ there are a lot of synonyms which can be met in literature or the conclusion of BONDS - experts: TVP, cervical transparency, width of a cervical fold, vorotnikovy zone, NT. Anyway it is about a congestion of hypodermic liquid on a back surface of a neck of a fruit. It is possible to measure thickness of this layer only in the I trimester of pregnancy (to 14 - y weeks) as in later terms this liquid, as a rule, resolves. Normal TVP has to be no more than 2,7 mm. Increase in this size is characteristic of a Down syndrome. Also at this pathology nasal stones at a fruit often are not visualized.
That was easier to be remembered when and what parameters have to be estimated, it is possible to use the provided table.
Needed to talk about results of prenatal screening: most of all questions and experiences of future mothers are connected with this subject.
Important detailsneeds to be known that concentration of b - HGCh, RARR, an estriola and AFP in blood can change not only at chromosomal pathology and DZNT, but also at other pathology of pregnancy: threat of interruption or spontaneous abortion, pre-natal arrest of development or death of a fruit, fetoplatsentarny insufficiency, late toxicosis (gestoz). Also the size of biochemical indicators is influenced by reception of gestagen (Dyufaston, Utrozhestan), mnogoplody.
to Compare results of the identical, but made in different laboratories analyses incorrectly as units of measure and norms often do not coincide. It is connected with the fact that for carrying out research in these laboratories are used different the test - systems. And for calculation of risks of pathology now there are several special programs with the norms too. And results of such important inspection as prenatal screening (where it was executed), has to have an opportunity to estimate any gynecologist. Therefore the obtained data are transferred to MEGOHM (special coefficient). Norma MOM for any biochemical markers, and also for the thickness of vorotnikovy space (TVS) - from 0,5 to 2,0.by
For adjustment of size MEGOHM and calculation of individual risk consider such factors as quantity of fruits, body weight of the pregnant woman, racial accessory, smoking, diabetes, use of auxiliary reproductive technologies (EKO). Taking into account these data individual correction of MEGOHM therefore receive “MEGOHM skorregirovanny value“ is carried out. It is used then for calculation of individual risks. Therefore all above-mentioned factors have to be reflected in the napravitelny form. As separate risk factor is considered age of future mother. It is connected with the fact that after 35 years the probability of the birth of the child with a Down syndrome increases.
the Nasal stone
Calculation of risk of chromosomal pathology at a fruit is carried out by
| to laboratories by means of special programs and is specified in figures. There is a threshold value of risk making 1:250. It means that the statistical probability of the birth of the child with chromosomal pathology (a Down syndrome, Edwards`s syndrome) makes 1 case from 250. Comparison of the received result with threshold value allows to allocate women of risk group by which additional researches have to be conducted. Reduction of figure in a denominator of this fraction is characteristic of increase in risk of congenital chromosomal pathology at a fruit (for example, 1:50 or 1:100). |
the Gynecologist estimates results of prenatal screening. At detection of any deviations the pregnant woman is directed to consultation to the geneticist. This expert resolves an issue of need and methods of additional inspection.