In Japan, it is commonly believed that pregnancy lasts for 10 months instead of the standard 9 months accepted in most parts of the world. This belief may have originated from a misunderstanding of how the lunar calendar works, as traditional Japanese culture defined a month as four weeks rather than a specific number of days. However, medical science states that the average duration of pregnancy is around 280 days or 40 weeks, calculated from the first day of the woman's last menstrual period. There are many factors that can affect the length of a pregnancy, including genetics, maternal age, health status, nutrition, stress levels, and environmental factors. Prolonged pregnancies beyond 42 weeks can pose risks to both mother and baby. In Japan, childbirth is typically managed by midwives who prioritize maintaining harmony between mother and baby during delivery. Pregnant women should be aware that due dates are estimates and not always accurate predictors of when labor will begin.