The possibilities of modern medicine allow the future mother to learn as much as possible about the course of pregnancy, to exclude possible deviations in her course, to determine the risk that something in the development of the baby will go wrong. Today, pregnant women have the opportunity, if they wish, and sometimes even when necessary, to undergo a wide variety of examinations and pass all kinds of tests that allow, with varying degrees of probability, to establish the absence of a threat to the normal and natural formation of the fetus. One of the complex methods of examining a pregnant woman is the so-called prenatal screening.
Second screening during pregnancy: terms
Screening research in the CIS is conducted relatively recently, but due to the rich information content it is actively used in the practice of pregnant women. The screening makes it possible to determine the risk groups for complications during pregnancy, and also makes it possible to identify the risk groups for the development of congenital abnormalities in the fetus. The first screening study is conducted in the first trimester, and the second screening during pregnancy, respectively, in the second trimester.
The most “successful” time for the first screening specialists consider the period of 12-13 weeks, although this study can be carried out from 11 to 14 weeks of pregnancy. The time frame for the second screening during pregnancy is from 16 to 20 weeks, although the most optimal and most informative for it, doctors call 16-17 weeks of pregnancy.
Second screening during pregnancy: indicators
The purpose of the second screening is to determine among pregnant women at risk when the chromosomal abnormalities in the fetus are quite high.
Screening can be ultrasound (reveals possible fetal abnormalities using ultrasound); biochemical (blood markers); and combined – consists of ultrasound and biochemical examinations. As a rule, an ultrasound examination is carried out as part of a screening study at the end of the second trimester of pregnancy, and the second screening during pregnancy itself consists in a blood test for various indicators. The results are taken into account and the ultrasound conducted on the eve of the screening of the second trimester of pregnancy.
The algorithm of actions during the screening is as follows: a pregnant woman after blood donation and an ultrasound scan fills out a questionnaire, where she indicates personal data on which the duration of pregnancy and the risk of developing defects will be calculated. Analyzes are carried out taking into account the duration of pregnancy, after which the computer program processes the obtained information to calculate the risks. And yet, even the results obtained cannot be considered a definitive diagnosis, after which one can absolutely talk about the presence of risks, if they have been established. For more detailed and accurate information, the doctor should refer the pregnant woman for additional tests and for consultation to the geneticist.
If we talk specifically about the second screening during pregnancy, it is a biochemical study of the mother’s blood by special tests. The so-called “triple test” is the analysis of blood levels of such substances as human chorionic gonadotropin (hCG), alpha-fetoprotein (AFP), free estriol. If the second screening during pregnancy also provides for a blood test for inhibin A, then the test is already called a “quadruple”. A study of the concentration of these specific hormones and proteins in the blood of a pregnant woman makes it possible with a certain degree of probability to talk about the risk of developing such developmental defects as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), neural tube defects (spinal canal injury and anencephaly) in the fetus. .
Second-trimester screening results may indirectly be a sign of some abnormal conditions for fetal development and pregnancy complications. For example, an elevated level of hCG may indicate chromosomal abnormalities, the risk of developing preeclampsia, or the presence of diabetes mellitus in the mother, and multiple pregnancy. Reduced hCG, in turn, may be a sign of abnormal development of the placenta. An increase or decrease in AFP, and with it inhibin A in the mother’s serum, indicates disturbances in the normal development of the fetus and possible congenital pathologies – defects in the open neural tube, the likelihood of trisomy 21 or trisomy 18. A sharp increase in AFP can also lead to fetal death . Changes in the level of free estriol – a female steroid hormone – can be a signal of impaired function of the placental system, an insufficient amount indicates possible impairment of fetal development.
Even if the results of the second screening during pregnancy are characterized as unfavorable, you should not despair and immediately sound the alarm. They only indicate a possible risk of anomalies, but they are not a definitive diagnosis. If at least one screening indicator does not correspond to the norm, it is important to undergo additional comprehensive research. In addition, some factors that change the results of the survey may affect the performance of a screening survey. These are: in vitro fertilization, weight of the pregnant woman, diabetes mellitus and any other diseases of the mother, bad habits, for example, smoking during pregnancy. In case of multiple pregnancies, it is not at all advisable to carry out a biochemical blood test as part of a screening: the results are too high, and the accuracy of the risk is extremely difficult to calculate.