One week of pregnancy is 7 days, and the entire pregnancy period is normally 280 days. If the menstrual cycle is usually regular, the number of days of pregnancy can be calculated based on the last menstrual period, i.e. from the first day of the last menstrual period, which is usually more accurate. If menstruation is irregular or the time of the last menstrual period is unknown, the week of pregnancy can be deduced from an early pregnancy ultrasound. The gestational sac can usually be detected around 35 days of pregnancy, and the germ and primordial heart tube pulsation can be detected around 49 days of pregnancy. In mid to late pregnancy, after 14 weeks of gestation, days of pregnancy need to be determined based on ultrasound data such as biparietal diameter, head circumference, abdominal circumference and femur length. Generally, delivery between 196-258 days of pregnancy is considered preterm, and delivery between 259-293 days of pregnancy is considered full-term. A pregnancy that is older than 294 days and has not been delivered is called a term pregnancy. If menstruation is delayed for more than 1 week and you have unprotected sex, you should consider the possibility of pregnancy. According to a 28-day menstrual cycle, a one-week delay in menstruation means that you are pregnant for 35 days, and it is recommended that you have regular obstetric checkups.