Par3 deficiency in the mother allows survival of Thbd^Pro/Proembryos, but these are growth retarded in utero and smaller at birth. Pregnancies of Par3^−/−FV^Q/QThbd^Pro/+ females mated to Thbd^Pro/+ males were analyzed at 15.5 dpc. Lengthwise cross-sectional area (A), length of the embryo (B), and placental cross-sectional area (C) were measured from digital photographs taken at a known magnification and resolution. Neonatal weight was taken within 18 hours of birth (D). P values were computed in comparison with Thbd^+/+ controls.