During sex, male penis penetration from behind is not going to have an adverse effect on the uterus. Rear penetration sex position is one of the very common sex styles. Usually, penetration from the back allows deeper entry and gives more pronounced sexual stimulation to the woman. The penis may touch the cervical opening and stimulate the uterus causing irritating contractions resulting in abdominal discomfort or slight pain in women, but mostly relieved after a short break. However, it is important to note that the top of the cervix should not be touched frequently to avoid causing cervical damage or cervical inflammation.