Delayed menstruation after the first coitus may be due to the following reasons: 1, to rule out the possibility of pregnancy, although only 1 coitus, if the coitus in the ovulation period may lead to pregnancy. It is recommended to use morning urine to do early pregnancy test after 5 days of delayed menstruation to rule out the possibility of pregnancy. 2, due to the first coitus may lead to emotional changes, there will be excitement, there will be fear, there will be worry, emotional changes may lead to endocrine temporary relative impact, so it will make the menstruation delayed phenomenon. If the test is not pregnant, you can observe for another 3-5 days, and if you still don’t have your period, you can take progesterone orally to promote menstruation.