I. What are chromosomes?
Chromosomes are the genetic material of an individual, on which thousands of genes are arranged, which determine the traits and phenotypes of the individual. Chromosomes are found in the nucleus of a cell and need to be removed by a specific method, placed on a glass slide, stained and then observed under a microscope, and a final diagnosis made.
Normal human cells have 46 chromosomes, which are paired into 23 pairs. Each pair of chromosomes is of bi-parental origin, i.e. one from the father and the other from the mother. 23 pairs of chromosomes work in concert to regulate the growth and development of the human body.
What is chromosome disease?
A large group of diseases caused by changes in the number or structure of chromosomes are called chromosomal disorders. The most common chromosomal disorder is Down syndrome (also known as trisomy 21 or congenital dysmorphism).
The usual manifestations of chromosomal disorders are mental retardation, often with a peculiar facial appearance, stunted growth, and sometimes with certain organ malformations. Chromosomal disorders are currently untreatable, and the affected child brings a large burden to the family and society, while the quality of survival of the affected child itself is seriously reduced, so it is necessary to make an accurate diagnosis before the birth of the affected child, and timely termination of pregnancy, which is the only way to avoid birth defects.
Third, can the fetus have chromosomal disorders if the couple’s previous generations are normal?
The majority of these syndromes are related to the age of the pregnant woman, and only a very small number of them are inherited from the previous generation, so the fact that the last few generations of the couple are normal does not guarantee that the fetus will not have chromosomal disorders. As the maternal age increases, chromosome pairing and separation may occur during the maturation process of the egg cells, and the egg cells with extra chromosomes will form a chromosomally abnormal fetus after fertilization with normal sperm.
Which pregnant women need fetal chromosome examination?
Some pregnant women whose fetuses are prone to chromosomal disorders after pregnancy are at high risk and need to undergo fetal chromosome examination, including the following pregnant women.
1, pregnant women of advanced age (age ≥ 35 years at delivery)
2, serum screening results showing high-risk features (including trisomy 21 high-risk, trisomy 18 high-risk or trisomy 13 high-risk)
3, abnormal ultrasound findings (e.g. fetal soft tissue thickening in the neck, missing nasal bone, choroidal cyst, strong echoes in the intestinal canal, strong light spot in the heart, widened renal pelvis, widened lateral ventricle, fetal edema, fetal malformation, etc.)
4. abnormal chromosomes (balanced translocation, inversion, chimerism, etc.) in the pregnant woman herself or her husband
5, pregnant women who have ever given birth to a deformed or chromosomally diseased child
6, pregnant women with a history of repeated spontaneous abortions
7. Pregnant women with low intelligence in the family V. What are the means of fetal chromosome examination?
At present, there are three main means.
Chorionic villus sampling: the earliest time, 60-80 days of pregnancy can be performed, once the fetal abnormality is found, the pregnancy can be terminated as early as possible, shortening the unnecessary waiting time, thus reducing the psychological and economic burden of pregnant women, but the risk of miscarriage is greater than that of amniocentesis.
Amniocentesis: It is the easiest and safest method of prenatal diagnosis, and can be done from 16 to 30 weeks of gestation, but the success rate of amniotic fluid cell culture is significantly lower when the gestational week is greater than 27 weeks.
Cord blood sampling: The advantage is that the culture time is short and the report can be obtained in one week, but it is technically difficult and the risk of complications is significantly higher than that of amniocentesis.