The most dangerous part of pregnancy is before the 12th week of pregnancy and after the 37th week of pregnancy, before the 12th week of pregnancy is the early stage of pregnancy, easy to miscarriage, after the 37th week of pregnancy, easy to fetal hypoxia and some obstetric complications. Just pregnant fertilized egg in the uterus bed is not solid, at any time there may be a miscarriage, if you do not pay attention to rest, fatigue and exhaustion, may lead to biochemical pregnancy or preeclampsia. Early pregnancy is also the period of embryonic nervous system development, such as exposure to some harmful substances, such as drugs or chemical products, the embryo chromosome may occur mutations, resulting in the development of embryonic malformation. In late pregnancy, the uterus enlarges and the fetus grows faster, making it easy for some obstetric complications to occur, such as placenta praevia and placental abruption. It is important to take rest and have regular checkups during these two periods to prevent accidents.