I. Analysis according to the characteristics of fetal development Within 2 weeks after fertilization, after the egg is laid, the drug has a “full” or “no” effect on the embryo. “All”: Harmful drugs destroy all or part of the embryonic cells, resulting in early death of the embryo and miscarriage. “The embryo can continue to develop without any abnormalities; 3 to 8 weeks after fertilization, the 15th to 25th day, the central nervous system is in the stage of differentiation and development; the 20th to 30th day The embryo is in the stage of differentiation and development of the head, spine, bones and muscles, and the emergence of limb buds; the 20th to 24th day is the stage of embryonic organ differentiation and development, the cells begin to develop directionally, and it is difficult to repair the damaged cells through differentiation and compensation, when it is affected by harmful drugs, it can produce morphological abnormalities and form malformation, which is the sensitive period of drugs, especially the high differentiation period within 8 weeks, which is also the highly sensitive period of drugs and has the greatest risk of teratogenesis. The risk of malformation is highest. From 9 weeks to full term, fetal growth, organ development and function are perfected, only the nervous system, reproductive system and teeth continue to differentiate, especially the differentiation, development and growth of the nervous system reach their peak in late pregnancy and neonatal period, when the effect of harmful drugs, due to poor liver enzyme binding function and high blood-brain permeability, resulting in fetal functional retardation (IUGR), low birth weight, functional behavior, abnormalities and preterm birth. The effects of harmful drugs on the fetus have resulted in delayed fetal development (IUGR), low birth weight, functional and behavioral abnormalities, and increased preterm delivery. There are almost no drugs that are absolutely safe during pregnancy, therefore, unnecessary drugs should be avoided as much as possible. Generally speaking, the time of taking the drug occurs within 3 weeks of pregnancy (3 weeks of menopause), which is called the safe period. Since the number of blastocyst cells is small at this time, once they are affected by harmful substances, the cell damage is difficult to repair and will inevitably lead to spontaneous abortion. There is no need to worry about having a deformed baby when taking the pill at this time. If there is no sign of miscarriage, it generally means that the medication has not affected the embryo and the pregnancy can continue. The period from 3 weeks to 8 weeks of pregnancy is called the hypersensitivity period. At this time, the embryo is most sensitive to the effects of drugs, and teratogenic drugs can produce teratogenic effects, but do not necessarily cause spontaneous abortion. If there is vaginal bleeding related to this, it is not advisable to keep the fetus blindly and should consider interruption of pregnancy. The period from 8 weeks to 4-5 months of pregnancy is called the medium-sensitive period, which is the period of further development and maturation of fetal organs and is more sensitive to the toxic side effects of drugs, but most of them do not cause spontaneous abortion and the degree of teratogenicity is difficult to predict. The decision to interrupt pregnancy at this time should be based on a comprehensive consideration of the toxic side effects of drugs and other factors, weighing the pros and cons before making a decision. If the pregnancy continues, amniotic fluid and ultrasound should be performed in the middle and late stages of pregnancy, and if fetal abnormalities are found, abortion should be induced; if chromosomal abnormalities or congenital metabolic abnormalities are found, depending on the severity of the condition and prognosis, the pregnancy should be terminated early or treated intrauterine. Above 5 months of pregnancy is called hypoallergenic period. At this time, the fetal organs have basically developed and the sensitivity to drugs is low, so obvious malformations do not often occur after the use of drugs, but developmental abnormalities or limited damage may occur in varying degrees, such as fetal growth retardation caused by Mildron, brain damage caused by phenobarbital, deafness caused by streptomycin and quinidine. At this time, medication must be taken with great caution. Some experts have said that “in the very early stages of pregnancy, inadvertent use of drugs, from the first day of the last menstrual period counted within 28 days of the use of drugs, basically the effect on the fetus is full or no effect, that is, the child to not abort, stay on the okay. A similar conclusion was reached for X-rays done in early pregnancy”