Normally, in the third trimester of pregnancy, the fetus is already taking on a human form and can be observed through ultrasound to have a developing head, limbs and trunk, but the systems are just beginning to develop and are not yet perfect and need to be observed dynamically. Before the third trimester, the embryo is not yet formed and is mostly a gestational sac or just starting to develop systematically. Before the third trimester is a very critical time for the development of the systems, so patients should try not to get sick, catch a cold or use medication, because some external factors during this period can easily cause problems in the development of the embryo’s systems, which may lead to miscarriage or fetal malformation. After the third trimester, the fetus has already taken on a human form, and all systems are basically differentiated and only further matured, so the impact of medication or illness is relatively small.