Q&A: How long does implantation bleeding occur?

Officially, implantation bleeding may not exist. A medical literature search for "implantation bleeding" in humans came up with only three articles—ever! The term is probably used incorrectly by health personnel to describe bleeding that occurs early in the first trimester.

When an embryo implants in the uterus, there is initially no blood supply from the mother. After several days, a connection with the mother's blood supply is made but by this time the embryo is "buried" under the uterine lining—in other words, it is no longer in the uterine cavity.

Bleeding that occurs during this time could be a sign of a possible miscarriage or a tubal pregnancy. It may be very brief and light such as spotting on one day only or it can be heavier or longer. Any heavy or prolonged bleeding should be reported to your doctor.