Counting Murine Corpora Lutea to Determine the Number of Oocytes Ovulated

One can determine if and how many oocytes have been ovulated in a female mouse by counting the number of corpora lutea (CL) on the ovaries during the process of preimplantation embryo collection. A simple method of harvesting the ovaries and observing with a dissecting microscope and top lighting is provided along with a description of how to recognize CL. As the embryos rarely, if ever, cross the uterotubal junction, this provides a measure of the maximum number of embryos expected to be recovered from each oviduct or uterine horn, a number that can be valuable in analyzing early lethal mutations.