Genetic Screening During Pregnancy

Under what conditions is genetic screening required during pregnancy? Some expectant mothers want to know before birth whether their baby is normal or not. Some pregnant women do not want tests during pregnancy, as they will not allow the pregnancy to be terminated even if there is an abnormality in the babies.

Prof. Dr. Ulun ULUĞ
Written by Prof. Dr. Ulun ULUĞ. 0 comments 4907 views

As physicians, we may request detailed genetic tests to be performed, especially in order to identify babies who will need treatment immediately after birth. For example, in the case of a diaphragmatic hernia where the intestines are in the chest cavity, it is necessary to know the problem in advance to provide the possibilities of operating the baby immediately during delivery.

However, genetic testing is expensive. Genetic disorders are so rare that it is not economically feasible to examine every pregnant woman. Relatively inexpensive screening tests have been developed to screen all pregnant women. Unfortunately, their reliability is not high. For example, 50% of genetic abnormalities are missed with routine ultrasonography (Major abnormalities are much less likely to be missed. Missed abnormalities are usually minor or difficult to recognize, fortunately in very rare disease states.

Genetic screening in pregnancy; Genetic research methods, amniocentesis

Examination of the mother and father-to-be

Families with a high probability of having a genetic disease in the family are examined by clinical geneticists, and chromosome maps of the mother and father-to-be are drawn if necessary. The genetic disease is detected, the rates of transmission to children and prenatal diagnosis possibilities, if any, are discussed. The advanced age of the mother and even the father increases the likelihood of genetic diseases in the baby.


Many major diseases can be diagnosed by ultrasonography before the baby is 14 weeks old. If there is a vital problem, this week is the appropriate week to have an abortion. In doubtful cases, amniocentesis is performed.

Triple test

This is a test by measuring the levels of three hormones called alpha-fetoprotein, b-hCG and estriol in the mother's blood and comparing this with the hormone values in thousands of women via a computer. Especially the development of the brain-nervous system, Down syndrome (3 instead of 2 chromosome number 21), trisomy 18 (one extra chromosome number 18) risk is determined in the baby. If the risk is high, more detailed analyzes (eg amniocentesis) may be required. It should be noted that this test should only be used for risk estimation. Cannot be diagnosed.


A small piece is taken from the baby's placenta (wife) with the help of a needle. Fetal tissues are separated and genetic research is done using these tissues. Chromosome mapping can be done immediately in 3-4 hours. An advantage is that genetic diagnosis can be made in the early period when the pregnancy is 10 weeks old.


A portion of 15-20 ml is taken from the liquid in which the baby is present. Generally, the process is done between 12-20 weeks. The disadvantage is that it requires a long time (7-15 days) as the cells in the taken liquid must be produced in the laboratory.


This method is used in the later stages of pregnancy (after 20 weeks). Especially, some blood diseases can be diagnosed by examining the blood sample taken from the umbilical cord and sometimes directly from the body. It is also a technique used to prevent infant deaths due to blood incompatibility.

Fetal leukocytes in maternal blood

In general, the placenta (partner) prevents the mixing of mother and baby blood. However, some of the baby's blood cells pass into the mother's circulation. These cells live for a long time in the maternal blood. It is found in the mother's blood even years after the child is born. These cells can be separated and some genetic problems can be solved using some very sensitive methods (PCR). For example, gender determination may be possible at a very early stage. It is a method that has not been widely used in the research phase yet.


An optical instrument such as a very fine needle (such as laparoscopic instruments) is inserted directly into the uterus through a thin incision made in the mother's womb, and the baby is visualized in the water-filled sac in which it floats. Photos can be taken. It can be done after 16 weeks. It is being done less and less as it is risky for the baby (3-5% baby loss) and with the development of other less invasive methods.

Genetic screening in pregnancy; Situations where detailed genetic research is required

Pregnant women aged 35 and over

When amniocentesis is performed for pregnant women older than 35 years, the risk of loss of pregnancy is lower than the risk of fetal anomaly and especially of childbearing with DOWN SYNDROME. Therefore, amniocentesis is recommended.

Having some genetic diseases in the family (Mongolian child-Down Syndrome etc.)

Some genetic diseases are observed more frequently in some ethnic groups due to the frequent marriages within the family. Sickle cell anemia is more common in people of African Mediterranean, Middle Eastern, Caribbean, Latin American or Indian descent. Tay-Sachs disease is common among Ashkenazi Jews.

Retarded child in family

Down syndrome (Mongolism) and Fragile-X syndrome are the two most common genetic disorders associated with mental retardation. However, mental retardation due to chromosomal anomaly is responsible for 35-40% of all mental retardation problems.

A family history of a genetic disease for which genetic examination is possible

Prenatal diagnostic tests have been developed for some diseases. Tay-Sachs, cystic fibrosis, Down syndrome, thalassemia, sickle cell anemia are among the most common.

Familial genetic abnormality recognizable by ultrasound

Congenital heart diseases, polycystic kidneys, Potter's syndrome and some congenital diseases can be diagnosed by prenatal ultrasonography. On the other hand, club foot, cleft palate, cleft lip, and some minor heart diseases (although they can be recognized ultrasonographically) are often missed.

Previous stillbirths, recurrent miscarriages, or child deaths in the 2nd trimester (3-6 months)

Often such problems are caused by trisomies, Potter's syndrome (hereditary kidney development problem).

Close kinship between prospective parents

All kinds of close relatives increase the probability of genetic diseases in children.

Maternal diabetes, phenylkenonuria or epilepsy

These diseases should be controlled before pregnancy. Otherwise, the baby may be injured.

Having a blood clotting disorder in any of the parents

Hereditary hemoglobin disorders or some hereditary blood diseases can cause death of the baby in the womb at 4-6 months.

Some drugs taken at the beginning of pregnancy

Some antibiotics, epilepsy drugs, drugs that affect blood clotting, hormones, steroids, cancer drugs

Taking alcohol or drugs during pregnancy

A condition called fetal alcohol syndrome happens in children of mothers who drink heavily. In addition to alcohol, some sedatives or narcotic drugs can also cause the same problem.

Down Syndrome

It is an inherited disease. Normally, human cells have 23 pairs of chromosomes. If chromosome 21 has 3 instead of the usual 2, it creates a series of disorders that are often accompanied by mental retardation. Trisomy 21, Mongolism, Down syndrome are other names. In the picture above you can see the typical facial expression of such a child.

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