Parents with normal chromosomes and embryos with abnormal chromosomes 4 and 8 may be caused by advanced maternal age, diseases suffered by the pregnant woman, adverse drug reactions and environmental factors. 1. Maternity of advanced age: If a woman is older when she is pregnant and her egg cells are aging, homologous chromosomes or sister chromatid monomers may not be separated during the transmission of genetic material, causing chromosomal abnormalities in the embryo. 2. Diseases of pregnant women: If pregnant women have bacterial or viral infections, malignant tumors, autoimmune diseases, etc. in the course of pregnancy, it may lead to chromosomal abnormalities in the fetus. 3. Adverse drug reactions: Pregnant women should not take medicines without authorization during pregnancy. If pregnant women take some medicines without authorization, it may lead to fetal gene mutation and chromosome abnormality. 4. Environmental factors: If a pregnant woman is exposed to some toxic or harmful chemicals during pregnancy, or is affected by physical factors such as radiation, it may lead to genetic mutation of the fetus, thus causing chromosomal abnormalities. Pregnant women should undergo regular prenatal checkups during pregnancy to monitor the health of the fetus and themselves at any time, and seek immediate medical attention if any discomfort occurs.