Normal pregnancy lasts for 10 months, but this 1 month is not calculated in 30 days, it is calculated in 28 days. This is due to the fact that most women’s menstrual cycles occur once every 28 days, so the duration of pregnancy is about 280 days, which is more than 9 months if calculated on the basis of 30 days a month, of course, this is calculated from the time of the woman’s last menstrual period. If the usual menstrual cycle is not very accurate, early or delayed, the time of pregnancy is also not accurate. If the usual menstrual cycle is 40 days, the woman’s ovulation will be delayed, and the pregnancy will take place in 40 weeks or more.