Down’s syndrome – a rare genetic disorder characterized by physical and mental developmental delays, often does not depend on heredity. In most cases, you can identify Down syndrome without resorting to special analysis, as the outward signs of pediatric patients are the same, many of them can be determined from birth.
There is a probability determination birth of a baby with a deviation even during pregnancy.
Let’s first talk about hormones and those protein fractions, exponents considered in the analysis and research.
AFP – alpha-fetoprotein – fruit is a specific protein that initially with 6 weeks of pregnancy is synthesized in the yolk sac of the embryo, and after 13 weeks of gestation in the fetal liver. Penetration AFP excreted fetal amniotic fluid and blood of pregnant mainly depends on the function of kidney and gastrointestinal tract fetus, and the permeability of the placental barrier. Increase or decrease in the content of AFP in comparison with the levels common in the normal course of pregnancy, is a sign of abnormal fetus.
To increase the level of AFP in serum and amniotic fluid cause a number of fetal anomalies (congenital absence of the kidney, duodenal atresia, gastroschisis, omphalocele, hydrocephalus, anencephaly, intrauterine fetal death, and others.). Growth retardation, which is accompanied by a breach of AFP production by the liver, leading to decrease in the concentration in amniotic fluid and blood serum of pregnant women. Reducing the concentration of AFP (twice on standards for a given gestational age) may be due to Down’s syndrome.
PAPP-A (pregnancy-associated plasma protein-A) – pregnancy-associated plasma protein-A blood. During pregnancy, PAPP-A is produced in the cells of the chorion (the predecessor of the placenta). This protein belongs to a group of immunosuppressants, and suppresses the immune response of the maternal organism to the developing fetus. The normal level of PAPP-A in 1 trimester of pregnancy in 99% associated with favorable pregnancy outcomes. Determining the level of PAPP-A in the serum used for the prenatal diagnosis of Down syndrome and other congenital malformations in the fetus. In this condition the level of PAPP-A is significantly reduced.
Chorionic gonadotropin is the first hormone that is synthesized by the trophoblast cells (tissue formed during the attachment of the ovum). Otherwise, the main hormone called HCG pregnancy. Since the early stages of pregnancy, hCG performs lyuteotropnuyu function, thereby maintaining, hormone production by the corpus luteum of the ovary and turns it (the corpus luteum) in the corpus luteum of pregnancy. Explained that the work of the corpus luteum of pregnancy is to develop progesterone as long as the function itself does not take the placenta. Indicators of the level of hCG have inertia in time, varying over a fairly wide range of individual. For example, already begun with spontaneous abortion and fetal loss HCG decreases very slowly, and for a while can give a positive result, which indicates normal hormonal function.
Reduced content of the hormone can be observed in the pathology of the trophoblast, which is often accompanied by a non-developing pregnancy or threat of interruption.
Elevated levels of the hormone may be due to multiple pregnancy, fetal chromosomal abnormality, trophoblastic process (molar pregnancy) and taking drugs that increase levels of progesterone in the blood.
Screening of the first trimester. Whether it is possible at this stage of pregnancy to determine Down syndrome analysis.
The purpose of the combined screening test in 1 trimester of pregnancy is to identify the risks of a number of pathological disorders in the development of pregnancy: a neural tube defect, a defect of the anterior abdominal wall, chromosomal abnormalities, which include Down syndrome (trisomy 21 pairs of chromosomes) and Edwards syndrome (trisomy 18 pairs ). This study is made between 11 and 13 weeks of pregnancy. In the 1st trimester screening test includes: definition-hCG, PAPP-A and nuchal translucency sonography at 11-13 weeks of pregnancy. When combined estimates of these parameters the diagnostic accuracy of 86%. In identifying the risk of fetal malformations produce cytogenetic diagnostics. In the 1st trimester is transcervical amnioscopy. During this procedure, produce chorionic villus sampling and conduct genetic research.
Screening II trimester. What analysis Down syndrome pregnancy when the period is the most effective.
In the second trimester combined screening is also used, which includes the definition of fetal ultrasound and maternal serum blood levels of four markers: AFP, unconjugated estriol (free), inhibin = A and hCG. The test is performed between 16 and 18 weeks of pregnancy. In the presence of Down syndrome analysis shows that in the blood of women in the second trimester of pregnancy, the average level of AFP and free estriol reduced, and the average level of hCG and inhibin-A on average 2-fold higher relative to normal values for a given gestational age. It should be noted that the increase in hCG without lowering the level of AFP is not regarded as a predictor of fetal chromosomal abnormalities. Increase of hCG in the blood serum in the II trimester of pregnancy is associated with a high risk of developing preeclampsia (late toxicosis), placental abruption, and others. Pathology of pregnancy in the III trimester.
An important component of a comprehensive diagnostic, along with tests for Down syndrome during pregnancy is fetal ultrasound.
The objectives of this study are:
–podtverzhdenie ongoing pregnancy
–otsenka length fetal nasal bone (with a genetic pathology of fetal nasal bone is shortened relative indicators for the duration of pregnancy or no)
–otsenka matching child’s size to the expected term of pregnancy and identification of fetal growth retardation or malformations
–otsenka length of humerus and femur (with chromosomal aberrations observed shortening of the long bones for 2 weeks or more, relative to the size appropriate for a given gestational age)
–vyyavlenie presence of three vessels in the umbilical cord (normal umbilical cord has three vessels: one vein and two arteries. When genetic pathology in 95% of cases, the umbilical cord has two vessels, one vein and one artery)
– Evaluation of the amount of amniotic fluid (the pathology of the fetus revealed oligohydramnios or no treatment)
According to testimony in the II trimester perform well and invasive diagnostics: transabdominal (through the anterior abdominal wall) aspiration placental villi and transabdominal cordocentesis (puncture of the umbilical vessels).