TERMINOLOGY
Cell: It is the smallest structural unit of the body.
Gene: DNA sections containing information that controls a person's physical characteristics and all body functions are called
'genes'. They are the basic units of heredity. It is passed from parent to child.
DNA: The genetic material passed from parent to child is DNA. They are carried in chromosomes.
Chromosome: These are the structures located in each cell that carry the genes that determine the structure of the person.
Sex Chromosome: These are the chromosomes that determine the gender of the person. In humans, there are two types: This change is called 'mutation'.
Carrier: A person who has no symptoms of the disease, but is likely to pass the disease to his/her child, is a 'carrier' for that disease.
Aneuploidy: It is the condition of having an abnormal number of chromosomes.
Monosomy: It is called missing one chromosome.
Trisomy: It is called the condition of having an extra chromosome.
Trisomy 13 (Patau Syndrome): Serious problems in the brain and heart, such as extra fingers, cleft palate-lip.
disease due to chromosomal disorder in which many structural anomalies are observed. Most of them die in the first year.
Trisomy 18 (Edwards Syndrome): It is a chromosomal disorder that causes serious mental retardation and physical problems (small head, heart
anomaly, deafness). Most of them are lost before birth while in the womb or
in the first month after birth.
Trisomy 21 (Down Syndrome): People who can live until adulthood, have abnormal physical features in their face and body, have low intelligence level. It is a genetic disorder in which and some diseases are common.
Fetus: It is the name given to the development process that continues from the 8th week of pregnancy until birth.
Placenta: It is the tissue that provides communication between the mother and her baby.
Trimester: Three thirds of pregnancy. It is the name given to the monthly period.
Prenatal: Prenatal period, pregnancy process
Ultrasound: It is the imaging method using sound waves to examine internal organs.
Neural Tube Defect: Brain, spinal cord or integrity of the skin covering these structures It is called
congenital structural defects that develop due to hair deterioration.
Nuchal Translucency (NT) (nuchal translucency) Scan: It is the test in which the thickness of the subcutaneous tissue at the nape of the fetus'
neck is measured by ultrasound. It is used to screen for some structural disorders such as trisomies and heart diseases
.
Screening Test: Test that looks for the risk of possible disease in those who have no signs or symptoms of the disease.
Diagnostic Test: Test that looks for the disease or its cause.
/> Amniocentesis: Taking some fluid from the sac surrounding the baby (amniotic fluid) with a thin needle for examination.
Chorionic Villus Biopsy: The process of taking a small sample from the placenta for examination.
What are genetic disorders?
Genetic disorders occur as a result of changes in genes or chromosomes. The situation of having one missing or one extra
chromosome is called 'aneuploidy'. Hereditary diseases occur as a result of permanent
changes in genes called 'mutations'. In most cases, both parents must carry the same disease
gene for the child to have the disease.
What is prenatal genetic examination?
These are tests that give parents information about the presence of some genetic disorders for their unborn babies.
What are the basic prenatal tests?
There are two types of prenatal tests for genetic disorders:
1. Prenatal screening tests: Determines the risk of aneuploidy and some additional disorders in your baby.
2 Prenatal diagnostic tests: It definitively determines the presence of aneuploidy or a certain hereditary disease
in your baby. In diagnosis, fetal cells in the fluid taken by amniocentesis or
placental cells taken by chorionic villus biopsy are used.
Pregnant women should be offered both screening and diagnostic test options.
What are prenatal screening tests?
br /> Screening tests determine the risk of some disorders in your baby:
1. Carrier status screening: A swab or blood taken from the inside of the cheek is studied to determine whether a person is a carrier for a certain disease.
2 Prenatal genetic screening tests: Pregnant women are screened for aneuploidy and structural anomalies using blood and ultrasound findings. It is applied in the 1st or 2nd trimester.
What is first trimester screening?
First trimester screening test includes maternal blood biochemistry and pregnancy ultrasound. 11-14 weeks
Also called screening test. This is done between weeks. Two biochemical substances are measured in maternal blood: free
beta-hCG and PAPP-A. In the fetus, the thickness of the subcutaneous transparency at the nape level is measured. An abnormal result means an increased risk for
Down syndrome or other aneuploidies (Trisomy 13 and trisomy 18). In addition, the fetus is evaluated in terms of basic structural anomalies (such as some heart, anterior abdominal wall, brain, skeletal anomalies,
midline anomalies) that can be detected in this
week.
What is second trimester screening? ?
1. Quadruple test: It is a screening test performed with both ultrasound and maternal blood. The risk of Down syndrome, trisomy 18 and NTD is determined by measuring four
different biochemical markers (estriol, beta-hCG, AFP, inhibin-A) in the mother's blood and the baby's head circumference by ultrasound. 15.-22.
2. Second level ultrasound is performed at 18-22 weeks, where structural anomalies in the fetus are evaluated. It is an ultrasound examination performed between
weeks. It is also called 'detailed fetal anatomical scanning'.
What is combined 1st and 2nd trimester screening?
1st and 2nd trimester screening test results can be combined in different ways. They give more reliable results than a single test result
. However, it should not be forgotten that the result will be known in the 2nd trimester.
What is free fetal DNA analysis?
Free fetal DNA is the DNA found outside the cell. During the formation of the placenta, some
baby's DNA is released into the mother's blood. It can be used as a screening test for trisomy 21,13,18 and sex chromosome number anomalies
. It is not recommended in multiple pregnancies. Care can be started at the 10th week of pregnancy. The result appears in one
week. A 'positive' result means 'increased risk'. Diagnostic work should be done. Among other screening tests, it is most commonly used as a second screening test in those who have an increased risk of having a baby with chromosomal anomaly. Other screening tests are still most suitable for pregnant women in the 'low risk group' for chromosomal anomaly. Because
this test is too expensive to be a screening test.
What do screening test results mean?
Tests that screen for aneuploidy express the probability of disease as a numerical risk. A 'negative' result means your baby has a 'low risk of disease'. Ha It does not eliminate the possibility of stagnation. A 'Positive' result means your baby has an 'increased risk of disease'. It does not necessarily mean that there is a disease.
Diagnostic procedures that provide definitive results are an option for all pregnant women. Your doctor or genetic
counselor will discuss with you what the test results mean and your next options to help you
make a decision.
How accurate are prenatal screening tests?
For each test ' There is a possibility of 'false positive' and 'false negative' results. If there is an 'increased risk' according to the test result when the disease is not actually present, there is a 'false positivity'. If the disease is actually present but the risk is low according to the test result, there is a 'false negativity'. Your doctor will help you understand the reliability of the test by giving these rates for each test.
What should I consider when deciding whether to have a prenatal genetic test?
It is completely your decision whether to have the test or not. Your personal beliefs and values
are important when making this decision. It will help to consider how you will use prenatal screening test results. Remember that a positive
result only indicates an increased risk. However, a diagnostic test is performed when you want a definitive result.
Some couples want to know in advance whether their baby will be born with a genetic disorder. This process
gives them time to become informed about the disease and plan their child's follow-up process. Some
couples do not want to continue the pregnancy if the disease is certain. Some couples do not want to know anything
before birth. In this case, the prenatal screening test is not taken, or even if it is done, the diagnostic test is not requested in the presence of a positive result
. There is no 'right' or 'wrong' decision. The decision is purely personal.
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