1, before and after pregnancy, pregnant women have a history of viral infections, such as influenza, rubella, etc.; Tips: You can diagnose whether a pregnant woman is infected with the above viruses through the “teratology five” test. The “teratology five”, also known as “eugenics five” or TORCH test, including: toxoplasmosis, rubella virus, cytomegalovirus, herpes simplex virus and other viruses. 2. At the time of conception, one of the spouses has a chromosomal abnormality; Tip: Doctors recommend that pregnant women over the age of 34 undergo an amniocentesis to check for chromosomal abnormalities in the fetus; pregnant women under the age of 34 can undergo a blood screening test to determine if the fetus has a chromosomal abnormality. Women under the age of 34 can undergo a blood screening test to check if their fetus belongs to a high-risk group for chromosomal abnormalities. Time of examination: maternal blood screening and amniocentesis should be performed in the middle of pregnancy, i.e., after 15 to 20 weeks. 3, one of the spouses is older; Related reading: women over 40 years old are three times more likely to have a miscarriage than women 25 years old. And new research shows that the probability of miscarriage increases greatly if the father is older than 35. 4, before and after pregnancy, pregnant women taking teratogenic drugs, such as tetracycline, etc.; 5, one of the husband and wife long-term radioactive screen work or work in a polluted environment; 6, a history of habitual abortion, preterm delivery or stillbirth of pregnant women; 7, one of the husband and wife long-term pet owners.