How is second trimester screening performed?
The second trimester of pregnancy for many women is marked by the conduct of screening, a triple test for chromosome pathologies of the fetus. This study is considered slightly less informative than that which is conducted at the end of the first trimester. But nevertheless biochemical screening of the 2 trimester and ultrasound can and are considered as objective data for the calculation of risks and even the establishment of an accurate diagnosis.
What is this research, what is its informativeness, can there be mistakes? Screening for the 2nd trimester is a complex of medical measures, a blood test from a vein and ultrasound, the results of which are entered into a computer program that calculates the risks of Down syndrome, Edwards, Patau, Turner, triploid and others.
In this case, deciphering the results of biochemical screening of the 2nd trimester is issued by the program in the form of quantitative risk. For example, Down Syndrome is 1: 1800. And this means that one woman from 1800 of the same age, with the same features of pregnancy, ultrasound and blood test, a child with this pathology is born.
Since simply the figures of risk for many women are not seriously taken, they decide to pass only part of this survey. Namely, ultrasound screening of the 2nd trimester, which can clearly show the developmental defects of the fetal organs and systems, suggest a genetic disease based on some markers, such as a shortening of the nasal septum or the absence of phalanx of the little finger. In addition, prenatal screening of the second trimester makes it possible to diagnose the obvious congenital malformations of the face, heart, stomach, brain and spinal cord, urinary system and kidney integrity. Many of these pathologies are indications for the artificial termination of pregnancy, since they are not subject to surgical treatment and make the fetus unsustainable. Also, some markers can be identified that indicate genetic abnormalities, but not always. For example, kidney pyeloectasia, hyperechoic inclusions in the heart, hyperechoic intestine, etc. These markers require a re-examination. And blood screening of the 2nd trimester is very useful in this case. But even if the results of screening are good, after 2-3 weeks ultrasound is repeated. It is very desirable to make an ultrasound expert class, consider problem areas including in 3D mode, so the information obtained will be more accurate.
Screening for the first trimester and second screening for pregnancy differ in the methods used. So, at the first screening it is very important to accurately observe the deadlines for the blood test and ultrasound. This must be done necessarily in one day. And the timing of the second screening for pregnancy for ultrasound and biochemical analysis are different. So, the future mother donates blood for alpha-fetoprotein (AFP), free in-hCG and extriol at a period of 16-18 weeks. Observe this deadline is mandatory! But ultrasound is most informative for a period of 20 weeks. However, only biochemical screening is effective by no more than 70%. That is, about 30% of the favorable results of blood tests are false-negative, those who gave them up will have children with Down syndrome or Edwards.
At the same time, unfavorable results of screening for the 2nd trimester are usually indicative of invasive diagnosis. On long terms it is either an amniocentesis (in 16-20 weeks) or a cordocentesis (more than 20 weeks). And amniocentesis is less dangerous in terms of complications in the form of spontaneous late miscarriage or premature birth. Sometimes it happens that the screening of the 2nd trimester of the norm on ultrasound shows, and a child with a syndrome is born ... The reason for this is the absence of any markers of chromosomal pathologies, poor visualization with ultrasound examination, and sometimes even a doctor's inattention.
Many women are poorly versed in how they do screening of the uzi of the 2nd trimester, blood tests are being given. And they try to pass these tests on their own. Errors in the timing, receive blood test results without calculated risks - all this makes screening completely unreliable. After deciphering the results of screening for the second trimester - this is the task of a special computer program, not a pregnant woman or even her doctor. By the way, to perform a biochemical blood test in this case is not necessarily all consecutive future mothers. Coupons are usually given only to those who had poor screening first, the second screening during pregnancy is of a clarifying nature.
It is necessary to pass this examination also to women older than 35-40 years, and regardless of whether they have their children, who suffer from alcoholism and (or) drug addiction, survived a severe viral disease in the early stages of gestation, those who already have children born with chromosomal pathology, with a closely related marriage, as well as taking medications that have toxic effects on the fetus.
Factors such as IVF, multiple pregnancies, maternal diabetes, too small or too large a woman's weight, and some bad habits can influence the accuracy of the results.