The entire pregnancy period is 280 days (40 weeks). In order to grasp the characteristics of the different stages of pregnancy, the whole course of pregnancy is clinically divided into three periods, which are usually referred to as early, middle and late stages. Early pregnancy: refers to the third month of pregnancy, i.e. before the end of the 12th week of pregnancy. Mid-pregnancy: refers to the 4th to 7th month of pregnancy, i.e. after the 13th to 27th week of pregnancy. Late pregnancy: refers to the 8th to 10th month of pregnancy, i.e. after 28 weeks of gestation.