When a woman is pregnant, an ultrasound examination indicates that the uterus is posterior and that a gestational sac is present in the uterine cavity, which means that the woman is pregnant and that the pregnancy is intrauterine, except that the position of the uterus is posterior. This indicates that the body of the uterus is facing toward the waist and not toward the front of the stomach, which is a normal position. Because the woman’s uterus may be in a posterior, anterior or flat position due to the pulling of the ligaments in the pelvis, if it is too posteriorly flexed, it is called retroflexion, which can interfere with the discharge of menstrual blood and has no effect on pregnancy.