Genetic Screening. Why and When Is It Needed?

Genetic Screening. Why and When Is It Needed?

Genetic Screening. Why and When Is It Needed?

Every expectant mother wants to be sure that her baby is healthy and is growing normally, and her pregnancy is uncomplicated. Modern technologies allow detection of pathological pregnancies in early stages that gives the opportunity to make effective, timely decisions.
Prenatal screening is a test, which is safe for both mother and unborn baby. It allows accurate measuring a level of risk for genetic diseases, as well as risks of complications during pregnancy. Especially prenatal screening tests are recommended for pregnant women, who fall into any of the following categories:
  • Over 35 years of age.
  • Ultrasound showed abnormal development of a fetus.
  • One parent is a carrier of a genetic disease.
  • Family already have a child or a close relative, who has an inherited disease or birth defect.
  • Even without knowing she is pregnant, a women took strong drugs, which are not recommended for pregnant women; underwent an X-ray examination or subjected to any radiation; found herself under stressful conditions.
  • Consanguineous marriage partners (e.g., second cousin marriage).
  • Family just wants to avoid the risk of having a baby with chromosomal disorders or abnormal development.
What diseases can be detected by screening?
  • Trisomy 21 (Down's syndrome);
  • Trisomy 13 (Patau's syndrome);
  • Trisomy 18 (Edwards syndrome);
  • Cornelia de Lange syndrome;
  • Smith-Lemli-Opitz syndrome;
  • Shereshevsky- Turner syndrome;
  • Triploidy of maternal origin;
  • Neural tube defects (anencephaly, spina bifida);
  • Omphalocele (umbilical hernia).
It should be mentioned that most of these diseases significantly affect the quality of life for both children and their parents. Some of them can be corrected, for example, the mildest form of spina bifida need no treatment; some defects can be completely eliminated by surgery, but in a number of cases, even after surgery, negative consequences can occur.
It is a mistake to think that chromosomal breakage syndromes are relatively rare and occur in one out of tens of thousands newborns. Some anomalies are really quite rare, but Down`s syndrome occurs in one out of 600-800 live births. However, even families that do not belong to any risk group can "lose out" in "genetic lottery".

When Are Prenatal Screening Tests Done?

Prenatal screening tests are performed twice, in the first and second trimesters of pregnancy. As mentioned above, in addition to assessment of the risks of genetic abnormalities, it allows prediction of possible complications during pregnancy, such as late toxicosis, placental insufficiency, intrauterine hypoxia, and premature birth.
The screening test of the first trimester is done at 11-13 weeks of pregnancy. In this period the embryo activity is small yet, but the placenta does work very well, so it can yield information, such as free hCG (human chorionic gonadotropin) and PAPP-A (pregnancy-associated plasma protein A). Indicators not conforming the criteria of gestational age may indicate a delay in fetal development or the risk of hypertensive states.
The first screening is combined with ultrasound to assess compliance with the fetal growth standards.
The second prenatal screening tests occur between 14 and 20 weeks; 16-18 weeks are considered to be the best period, because it is during this time of development multiple disorders can occur. A complex combination of indicators such as placental hCG, values for alpha-fetoprotein (AFP) in fetal and free estriol, which characterize the placenta, fetus and woman's condition, is assessed. The second screening tests give detailed information on the fetoplacental system function.

Testing Results

It is important to remember that falling into a risk group is not a diagnosis. For its confirmation (or refutation) more tests, such as amniocentesis or chorionic villus sampling are needed. Pregnant women, who were excluded from the risk groups due to screening test results, do not require additional testing.

Are Prenatal Screening Tests Necessary if a Woman in Any Case Wants To Continue Her Pregnancy?

Screening tests can not only determine the risk of chromosome abnormalities in unborn baby, but also can diagnose and prescribe timely treatment of various complications of pregnancy. Prevention of complications identified through screening tests helps to prevent many complications of the last trimester of pregnancy, and, may be, save the life and health of a baby.