What is a curettage/vacuum aspiration and is it necessary after medical abortion?
Vacuum aspiration or curettage or dilation and curettage (D&C) is a surgical intervention to remove the contents of the uterus. Sometimes this treatment is necessary if there are complications after medical abortion or spontaneous miscarriage.
You do NOT need a vacuum aspiration if the ultrasound shows that there are still some small remains in the uterus (incomplete abortion) or experience some bleeding after 3 weeks AND you do not have any complaints like pain, fever or heavy bleeding. Small remains in the uterus can be treated with an extra dose of Misoprostol (2 tablets) or you can just wait until your next menstruation. The uterus will most likely empty itself. Regular menstruation comes back 4 to 6 weeks after a medical abortion. After a normal menstruation, you should not have any remaining tissue left over in the uterus.
However, in case you do have complaints like fever, persistent pain and heavy bleeding, a surgical intervention called vacuum aspiration is needed. Some doctors still only do a procedure called D&C or sharp curettage. This should not be done!! So, ask the doctor what kind of procedure she/he uses because they should perform a vacuum aspiration and not a sharp curettage or D&C (vacuum aspiration is less painful and has less risks).
All procedures should be done under local or general anesthesia! 
 "Frequently asked clinical questions about medical abortion", WHO; Pauleta JR, Clode N, Graça LM, Expectant management of incomplete abortion in the first trimester, Int J Gynaecol Obstet. 2009 Mar 28.