Mummified fetus in a mare.

This study details the case of a 12-year-old Arabian mare that, despite a history of embryonic losses, carried a nonviable fetus to term with the aid of progestogen. The mare eventually gave birth to a mummified fetus, shedding light on the role of hormone administration in retaining nonviable fetuses and the need for effective monitoring during gestation.

Case Background

• The subject was a 12-year-old Arabian mare with a past marked by repeated early embryonic losses. Regardless of her prior reproductive history, she gave birth to a mummified fetus.
• The paper explicitly states that this unusual birth was not the result of a twin pregnancy.

Progestogen Use During Pregnancy

• The mare had been receiving progestogen treatments throughout the gestation period. Progestogens are a type of hormone crucial in maintaining pregnancy by stimulating the lining of the uterus to prepare for fertilization and supporting the early stages of embryo development.
• The mummified fetus was expelled around the 325th day of gestation, which happened to be roughly two weeks after the ending of progestogen treatment.
• The study establishes that the use of progestogen beyond the initial 100 days of gestation could potentially foster the retention of a nonviable fetus.

Estimation of Fetal Age and Viability

• Based on the mummified fetus’ size, researchers estimated that the fetus stopped developing at around five months into the gestation.
• The researchers highlight that if the mother’s body, specifically the fetoplacental unit—the organs and tissues involved in fetal development— are unable to produce enough progestogens for pregnancy maintenance, they are also likely unable to supply sufficient oxygen and nutrients to meet the growing fetus’s needs.
• This leads to the idea that the fetus became nonviable due to inadequate nourishment and oxygen supply, eventually leading to its mummification within the womb.

Significance and Future Implications

• The findings underscore the importance of consistent and effective monitoring of fetal viability during horse pregnancies.
• Prolonged retention of a nonviable fetus can lead to complications for the mare and potentially for future pregnancies, demonstrating the need for early detection and appropriate response.