Mummified fetus in a mare

A 12-year-old Arabian mare with a history of repeated early embryonic losses gave birth to a mummified fetus. The fetus was not the result of a pregnancy with twins. The mare had been given a progestogen throughout gestation and expelled the mummified fetus at about 325 days of gestation, 2 weeks after progestogen treatment was discontinued. We estimate that the size of the fetus was consistent with a fetal age of 5 months. The mare and mummified fetus illustrated that progestogen administration after 100 days of gestation can promote retention of a nonviable fetus. When the fetoplacental unit is incapable of producing progestogens in adequate amounts for pregnancy maintenance at that stage of gestation, then it is also unlikely to provide sufficient oxygen and nutrients to meet the needs of the growing fetus. Monitoring fetal viability would enable practitioners to prevent prolonged retention of a nonviable fetus.