The period from the formation of the fertilized egg to the birth of the baby is forty weeks. The gestational week is calculated from the first day of the last menstrual period. Within ten weeks of gestation, i.e. eight weeks after fertilization, it is called the embryo and is the period of organ differentiation and formation. From the eleventh week of gestation, i.e. the ninth week after fertilization, it is called the fetus and is the period of growth and maturation. The process of embryonic development, as manifested in the following points: 1. The egg is fertilized in the abdomen of the fallopian tube, and after forming a fertilized egg, it undergoes cell division while running along the fallopian tube in the direction of the uterus. Two to three days after fertilization, it reaches the uterus, at which time the embryo is a blastocyst and takes up residence in a suitable location in the uterine cavity; 2. About one week after conception, the implantation is complete and the egg develops there. At about two weeks of gestation, the egg is still called a fertilized egg; 3. At about four weeks of gestation, the embryonic disc and the body tip can be identified; 4. At about eight weeks of gestation, the embryo takes on its first human form, and at this time the embryo shows a large head, accounting for nearly half the size of the entire fetal body, and can distinguish the eyes, ears, mouth, nose, toes and fingers, and the organs are developing, and the heart has been formed; 5. At about twelve weeks of gestation, the embryo has grown into a fetus, and the external genitalia have The sex can be initially identified, and the fetus can move its limbs. Early pregnancy is vulnerable to external stimuli, such as drugs, radiation and other harmful factors, which may lead to fetal malformations. Therefore, in early pregnancy, pregnant women should pay attention to rest, consult their doctors when taking medication and stay away from radiation.