Thbd^Pro/Pro embryos survive pregnancies of FV^Q/QThbd^Pro/+ females if the mother is treated with LMWH or is deficient in Par3. Thbd^Pro/Pro (B,D) and littermate Thbd^Pro/+ (A) and Thbd^+/+ (C) embryos from representative pregnancies treated with LMWH (A-B) or with maternal Par3 deficiency (C-D) are shown. These correspond to 16.5 dpc for LMWH treatment and 15.5 dpc for maternal Par3 deficiency. Thbd^Pro/Pro embryos are growth restricted in pregnancies of Par3^−/− FV^Q/QThbd^Pro/+ females (measurements shown in Figure 3A-B). Their placentae tend to be smaller (measurements in Figure 3C) but do not present evidence of overt thrombosis. Hematoxylin-eosin stained histological sections of Thbd^+/+ (E) and Thbd^Pro/Pro placentae (F) corresponding to (C) and (D), respectively, are shown. The plane of sectioning is through the center of the placenta and perpendicular to its flat surface. Regions of the placenta are marked. Scale bars represent 5 mm in (A-D) and 1 mm in (E-F). db, decidua basalis; jz, junctional zone corresponding to basal plate in human placenta; lb, labyrinth or fetal placenta containing trophoblast-covered fetal vessels bathed in maternal blood.