The reason why you can have sex when you are about to have your period is as follows: 1. Before you have your period, the endometrium is not yet shed, although the pelvis is already in a state of congestion, the mucous membranes of the reproductive tract are also congested, so you can have sex at this time. But pay attention to the action of sex can not be rough, because in the case of congestive state, if the action is rough, may cause local damage to the mucous membrane. 2, in the menstrual period before the coitus will not lead to pregnancy, because the menstrual period is a regular situation, this time has been discharged egg, and the egg can only survive for 24 hours after discharged, so in the menstrual period before the time of the egg has been dead, this time there are Sex at this time will not cause pregnancy. No matter when you have sex, it is recommended to pay attention to sexual hygiene to avoid infection.