Surgical abortion is more damaging than natural abortion. Abortion is often performed by negative pressure suction, which is used to suction the pregnancy tissue out of the uterine cavity. If there is uterine manipulation, it can damage the lining of the uterus. If the lining of the uterus is damaged, it can cause adhesions in the uterine cavity and decreased menstrual flow. However, not all abortions cause this, there is just an increased risk of damage with an abortion. If a spontaneous abortion is followed by a complete miscarriage with no uterine residue, the patient is relatively safe because there is no damage to the endometrium. There is another type of natural abortion that does not abort cleanly, with a small amount of residue in the uterine cavity, which may need to be cleared again, and as long as there is a cleansing procedure, there is a certain amount of damage to the uterine lining, so surgical abortion is more damaging than natural abortion.