Screening for Down Syndrome and other chromosomal anomalies during pregnancy
Some of the factors harmful to the fetus during pregnancy originate from the fetus itself. Fetal chromosomal anomalies and especially Down syndrome have an important place among these. A significant portion of embryos and fetuses carrying chromosome disorders are lost through spontaneous miscarriages, but some of them continue until birth and are even compatible with life.
6 out of every 1000 newborns carry a chromosomal anomaly. In the majority of them, mental and physical retardation and system anomalies create serious problems for the family and society.
The incidence of Down syndrome increases with maternal age.
Maternal Age
The frequency of Down syndrome increases as the mother ages. The frequency of giving birth to Down syndrome babies in society is 1.3 per 1000 births. This rate is 1/1351 for 25-year-old mothers, 1/909 for 30-year-old mothers, 1/384 for 35-year-old mothers, 1/112 for 40-year-old mothers and 1/28 for 45-year-old mothers.
For this reason, amniocentesis is recommended for older mothers for the diagnosis of babies with anomalies.
Biochemical tests performed to recognize Down Syndrome
For the first time in 1984. Studies conducted in 2017 showed that AFP, Estriol and hCG hormone levels in the mother's blood are related to chromosomal disorders and that the levels of these hormones change in the blood of mothers carrying abnormal babies.
Thus, for the first time in England, they developed the test based on maternal age, AFP, hCG and uE3measurement in maternal blood, and with this test, 58-61% of fetuses with Down syndrome They stated that /strong> can be recognized.
When performing a screening test, ultrasonography is used to determine the gestational age.
In screening tests, not only Down syndrome but also Trisomy 18 disease, called Edwards syndrome, is screened.
With each week of pregnancy, AFP, hCG and uE3values in the maternal blood change. There are other factors that affect these hormone levels other than maternal age. These are the mother's weight, the mother's ethnic origin, and whether the mother has diabetes.
These factors are included in many screening tests. Risk calculation is made by taking this into account. After the risk calculation is made as a result of the screening test, the risk is determined as high or low by using a certain limit value. Generally, this limit value varies between 1/200-1/300. Advanced diagnostic tests are recommended for women whose risk is above this limit value. These are tests called amniocentesis and conion villus biopsy. In amniocentesis, the amniotic fluid containing the fetus is reached and the fluid is removed, and the cells belonging to the fetus are produced there and chromosome analysis is performed.
In conionvillus biopsy, cells are collected by reaching the fetus' placenta with special needles, and these are multiplied and chromosome analysis is performed.
Antenatol screening tests are also used to detect chromosomal disorders called Trisomy 21 and Trisomy 18, as well as spinal defects called neurol tube defects.
2-way, 3-way and 4-way screening tests
The test performed in the first trimester of pregnancy is known as the double test.
In the second trimester of pregnancy, the tests known as the triple or quadruple test are performed.
Double testing is done between 11-14 weeks. The nuchal thickness of the fetus is also measured during ultrasound. Risk calculation is made with nuchal translucency and two hormonal values checked in the mother's blood.
Triple and quadruple screening tests are performed between 14-22. It can be done between weeks of pregnancy. The 16th week is the week of pregnancy where the healthiest results can be obtained. In the quadruple test, in addition to the hormones mentioned above, the hormone called Inhibin A is additionally checked. The sensitivity of detecting Down syndrome is 81%. Thus, the reliability of the test increases. The advantage of the dual screening test is that it allows early diagnosis of the disease, if any.
Ultrasound scanning
It is a well-known fact that a significant portion of Down syndrome babies have congenital anomalies. Some of these anomalies can be detected by ultrasound in the intrauterine period. It is recommended that ultrasonographic screening be performed at 18-20 weeks.
The main ultrasonographic anomalies seen in fetuses with Down syndrome are:
Disorders related to the nervous system:
strong>
Cysts in the head occur when some normally existing spaces in the brain are filled with fluid. It can be observed that it grows.
Disorders related to the Head and Neck region:
Large tongue, cystic spaces seen at the nape of the neck, increased neck thickness, cleft lip or palate.
Disorders in the Cardiovascular System:
It can be observed that the vessels entering and exiting the heart are structurally deteriorated or there are structural disorders in the chambers of the heart.
Disorders in the gastrointestinal system
Bright appearance of the intestines, stenosis or developmental disorders in some intestinal sections may be observed.
With the urogenital system. Related disorders:
Enlargement and urine accumulation in the kidneys of the fetus may be observed
Disorders in the skeletal system:
Arm, Shortness of the leg bones and a gap between the big toe and second toe can be observed.
Excess water
Again, in pregnancies with Down syndrome, it can be observed that the fetus has a lot of water.
Growth retardation
Therefore, it is important to perform second-level detailed ultrasonography to recognize fetuses with Down syndrome or other genetic anomalies. If one of the anomalies mentioned above is observed during ultrasonography, other anomalies should also be carefully looked for.
Read: 0
