Intrauterine bleeding occurred in female homozygous FXIIIA KO mice. (A-B) Overview of the uteri of FXIIIA KO mice that spontaneously died of excessive vaginal bleeding. Sizes of embryos were uneven within the same uterus of a single animal (A). Both uterine horns were filled with blood and degenerating placentas (B). (C-D). Bleeding in the uterine cavity of KO mice killed at 10 dG. Both uterine horns for most embryos showed severe bleeding in one mouse (C), whereas a uterine shell for a single embryo in another mouse had a pool of blood (D). A bold line shows the border of excision for histologic examination. (E) The portion surrounded by a red circle is magnified in panel F (original magnification, × 40 [panel E] and × 200 [panel F]). (F) There is a region of hemorrhagic necrosis (area II) in the labyrinth adjacent to a blood pool (area I).