During the development of the embryo in the early stages of pregnancy, some people may experience embryonic arrest or miscarriage, which is mostly due to chromosomal abnormalities of the embryo. What are the causes of chromosomal abnormalities in embryos? Let’s learn together. 1, meiosis abnormal meiosis refers to the process of sex cell division to form sperm and egg cells. Under normal circumstances, sex cells will divide by meiosis to form egg cells and sperm with only half of the chromosomes (22 autosomes and 1 sex chromosome). If the chromosomes do not separate during meiosis or if some of the chromosome structures exchange places, the chromosomes of the sperm and egg will be abnormal, and the embryo formed after the sperm-egg union will also have chromosomal abnormalities. 2, mitotic abnormalities Mitosis is used to describe the process of cell development other than egg and sperm cells. Under normal circumstances, mitosis leads to a doubling of the number of chromosomes in the cell, and the chromosomes are then equally distributed to the two cells after cell division, restoring the normal number of 46. After the formation of the fertilized egg, the embryo begins mitosis, and the whole process repeats itself over and over again throughout our lives. During pregnancy, if mitosis occurs in error and the chromosomes are not divided into two equal parts during cell division, an abnormality in the chromosomes of the embryo will be formed. Environmental factors A good environment is necessary for the normal growth and development of the embryo. Exposure to teratogenic substances during pregnancy may lead to fetal development defects and embryonic chromosomal abnormalities. Some of the main teratogenic substances include: (1) certain drugs; (2) tobacco; (3) alcohol; (4) toxic chemicals; (5) some bacteria and viruses; (6) radiation. In addition to the above factors, advanced age, family history or previous births with chromosomal abnormalities are all high risk factors for embryonic chromosomal abnormalities. There is no effective treatment for chromosomal abnormalities in embryos, so it is necessary for couples who are preparing for pregnancy to have a good preconception checkup and to have a timely genetic diagnosis, such as chorionic villus sampling and amniocentesis, during the maternity checkup. For some IVF patients with unexplained recurrent miscarriages or repeated embryo implantation failures in IVF, they can try third generation IVF, that is, genetic analysis before embryo transfer to select healthy embryos for transfer in order to reduce the occurrence of embryonic abortion and miscarriage and obtain a healthy baby.