The main effect of having intercourse without knowing you are pregnant is to cause a preterm miscarriage. When you don’t know you are pregnant, it is usually in the early stages of pregnancy. At this time, the gestational sac has just formed and is still very unstable, so intercourse can easily stimulate contractions and cause a preterm miscarriage. After finding out you are pregnant, take rest and observe for vaginal redness or abdominal pain. If this happens, go to the hospital as soon as possible for birth control treatment. After finding out that you are pregnant, you can go to the hospital for an ultrasound to check the blood values of progesterone and human chorionic gonadotropin, and it is best to be prepared for birth control. Women should avoid intercourse during pregnancy, especially in early and late pregnancy, to avoid causing miscarriage or preterm delivery. If there is no sign of pre-eclampsia after pregnancy is detected, it is important to relax, take care of rest, strengthen nutrition and avoid physical labor. Intercourse, in general, will not have an adverse effect on the growth and development of the fetus.