Having a healthy baby is the dream of all mothers. Until about two decades ago, it was not possible to easily diagnose fetal abnormalities during pregnancy, and except in special cases and in special centers, it was not possible to assess the health status of the fetus. Fortunately, thanks to the advancement of medical diagnostic, laboratory, and imaging techniques, this possibility has been provided in many medical, laboratory, and imaging centers in many medical centers; In a way that many chromosomal abnormalities can be detected in the embryo with great accuracy and sensitivity. These tests are called screening tests. Screening tests are used for early detection of some chromosomal abnormalities, the most important and most common of which is Down syndrome, which in the past was called Mongolism …

Down syndrome

The human body is made up of millions of cells. All of these cells have a nucleus that acts as a command center. The nucleus of each human cell has 46 strands (23 pairs of similar double strands) called chromosomes. When the number of these chromosomes is disrupted or some of them are destroyed or altered, abnormalities will occur in the fetus. In Down syndrome, there is one extra chromosome 21 than normal, meaning that there are three chromosomes 21 in the cell nucleus. Heredity has no role in the development of this disease and usually the patients are born in families that do not have a specific history of this disease. Statistics show that one in every 500 live births is born with Down syndrome.

The life of people with this disease is not very short and half of people with Down syndrome live up to the age of 60. People with Down syndrome have different symptoms. The most important symptom in these children is severe mental disability, which is seen along with heart problems, vision and hearing disorders, growth, appearance and limbs. For early detection of this disease, it is better to use a screening test. The most popular of these tests are quadruple and combination tests.

Maternal age and risk of Down syndrome

The probability of having a baby with Down syndrome is not zero in any pregnancy, but the risk of this type of birth increases with the age of the mother, which is why the age of the mother is used as one of the important factors in calculating the risk of Down syndrome. So if the results of four tests on two mothers, one of whom is younger, are the same, the risk of having a baby with Down syndrome is higher in an older mother.

Quadruple Experiments

The four tests include measuring four different substances in the mother’s blood sample. These include beta-HCG, inhibin A, unconjugated sterile hormone, and alpha-phytoprotein. Quadruple tests can be done between 15 and 22 weeks of pregnancy, but the best and most accurate time is between weeks. 16 to 18 pregnancies.

Combination experiments

Free beta-HCG hormone

Article PAP A (PAAP-A)

In the mother’s blood is accompanied by ultrasound. Performing this type of ultrasound requires special experience because this type of ultrasound is intended to measure the thickness of the crease behind the fetal neck, which is called NT for short. The combination test can be done at 10 to 13 weeks of pregnancy, but the best time to do it is the 11th week of pregnancy.

Application of quadruple and combined experiments

These studies have two important applications:

Early diagnosis of Down syndrome

Early detection of neural tube defects

Neural tube defects refer to developmental abnormalities in the brain as well as the spinal cord and spine. When neural tube defects occur abnormally in the formation of the brain and skull, it is called anencephaly. Babies with these abnormalities die either during the fetal period or shortly after birth. Abnormalities in the formation of the spinal neural tube, sometimes with clefts of the spine, cause dysfunction of the nervous system in the lower parts of the body. People with these disorders may suffer from weakness and paralysis of the lower extremities, urinary incontinence or defecation.

By performing quadruple and combined tests, a large number of these cases can be detected before delivery.

Accuracy of detection of quadruple and combination tests

As mentioned earlier, quadruple and combination tests are included in screening tests and, like all other screening tests, are not able to detect 100% of the abnormalities.

These tests:

Almost all cases of encephalitis are diagnosed.

8-9 cases out of 10 fetuses with Down syndrome are identified.

8 out of 10 fetuses with neural tube defects are identified.

The meaning of this sentence is:

Quadrupole and combination screening tests are not able to detect 100% of fetal abnormalities during pregnancy.

Interpretation of quadruple and combination tests

The results of quadruple and combined tests do not give us a definite positive or negative answer, but based on the results, pregnancies can be classified into high-risk and low-risk pregnancies in terms of the risk of giving birth to a baby with fetal abnormalities. 

High risk group

When the result of screening tests for Down syndrome is considered positive, the risk of birth in a baby with Down syndrome is more than 1 case in 250 births. This is where the fetus is at high risk for Down syndrome. When the pregnant mother is included in the studies performed in this group, she should undergo more and more advanced examinations. Among these methods can be damp