Final answer:
The most common uterine abnormality contributing to abortion is uterine fibroids, which are noncancerous growths that can interfere with implantation or growth of the embryo and lead to miscarriage.
Step-by-step explanation:
The most common uterine abnormality contributing to abortion is uterine fibroids. Uterine fibroids are noncancerous growths of the uterus that often appear during childbearing years. They can disrupt the normal architecture of the uterus, interfering with implantation or growth of the embryo. Uterine fibroids can also cause changes in the blood flow and lead to inflammation or alterations in the uterine lining, which may result in miscarriage. Although other uterine abnormalities such as bicornuate uterus, uterine septum, and unicornuate uterus might also contribute to abortion, uterine fibroids are more frequently encountered in the general population and are a common cause of infertility and pregnancy loss.