Retained fetal membranes in C57BL/6NCrl mice: description of clinical case presentations and related epidemiologic findings.

During a triinstitutional study to test whether individually ventilated caging systems impaired welfare and reproduction relative to static housing systems, varying numbers (2 to 7) of discoid-shaped, fleshy structures were found in utero of 17 postpartum female mice on study. Further investigation revealed these structures to be retained fetal membranes (RFM). A point prevalence of 24.