Miscarriage is when a pregnancy spontaneously aborts because the developing baby has died. It occurs in around one in four pregnancies and usually doesn’t affect the woman’s ability to become pregnant again. A woman is classed as having recurrent miscarriage if she has three or more miscarriages in a row. She may then require help from a fertility specialist.
Some women have slight bleeding during pregnancy, called spotting, that gradually stops and does not harm the baby. However, if bleeding is accompanied by pain or it becomes heavier, you may be having a miscarriage. You should visit your doctor in any case to check whether you are having a miscarriage.
Bleeding that resolves may have been a "threatened miscarriage" and can be caused by bleeding from the placenta, fibroids in the uterus, sexual intercourse, or may be implantation bleeding (caused when the embryo implants into the uterine wall).
https://www.empowher.com/miscarriage/content/miscarriage-symptoms-and-management