Implantation bleeding
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If you experience vaginal bleeding during the early part of your pregnancy, the first thing you probably feel is fear. There are, however, many reasons you might see blood, and Obstetrician/Gynecologist David Barrere explains one of the causes could be implantation bleeding.
Your question
Can you tell me why implantation bleeding occurs, and what it looks like? How common is it?
The expert answers
The cells that eventually form the placenta are called trophoblasts. Specialized trophoblasts, the syncitiotroblast, are responsible for developing an interface with the maternal circulatory system to provide nutrients and allow gas (oxygen [O2] and carbon dioxide [CO2]) exchange to occur.
Periodically, while this interface is developed, some of the maternal blood is lost. This implantation bleeding is typically short in duration and quite light.
Approximately one third of all pregnant
women report bleeding that is associated
with implantation. The presence of
implantation bleeding does not increase the
overall risk of miscarriage, however. Most
pregnancies will continue until term without
further bleeding.

