08-05-2024

Horse miscarriages offer insights into human pregnancy loss

Earth.com staff writer

A recent study has revealed that 42% of miscarriages and spontaneous abortions in horses during the first two months of pregnancy are caused by triploidy, a condition involving an extra set of chromosomes.

This finding is significant because horses share many chromosomal and pregnancy-related similarities with humans, making them a valuable model for studying reproductive issues.

Primary cause of pregnancy loss

Mandi de Mestre, a professor of equine medicine at Cornell University, noted the rarity of reported triploidy in mammals other than humans during early pregnancy. “Over that embryonic period (up to eight weeks from conception), triploidy had rarely been reported in mammals outside of women,” she said.

“The study tells us that over the first six weeks of gestation, this will likely be the primary cause of pregnancy loss following natural conception.”

De Mestre is the corresponding author of the study titled “Naturally Occurring Horse Model of Miscarriage Reveals Temporal Relationship Between Chromosomal Aberration Type and Point of Lethality,” set to be published in the Proceedings of the National Academy of Sciences.

Horses as a model for human miscarriages

Human miscarriages, occurring in 10-20% of pregnancies, are often linked to chromosomal errors. However, finding a suitable animal model that mirrors the human condition has been challenging.

This study not only sheds light on the causes of pregnancy loss in horses but also highlights their potential as a model for understanding human miscarriage.

“We were able to study the impact of chromosome errors across the entire pregnancy in the horse,” de Mestre said. “We found that triploidy is only associated with losses in early pregnancy.”

Pregnancy loss in horses

The research involved examining 256 fetus and placenta samples collected over ten years from veterinarians treating horses with failed pregnancies. The samples were analyzed to determine the prevalence of various chromosomal abnormalities associated with pregnancy loss.

The findings showed that chromosomal errors were present in 57.9% of pregnancy losses up to day 55 of gestation, 57.2% of losses between days 56 and 110, and only 1.4% of losses from day 111 to the end of pregnancy.

The study also revealed that aneuploidy, involving the loss or gain of a whole chromosome, was primarily associated with miscarriages in the first 10 weeks, while partial chromosome deletions or duplications were linked to miscarriages occurring after 110 days.

These results closely parallel findings from large studies on human pregnancies, reinforcing the relevance of horses as a model for human chromosomal errors.

Early miscarriage in humans

Horses are particularly suitable for studying human pregnancies due to their similar gestation periods – 11 months in horses compared to nine months in humans – and the comparable rate of early embryo development.

Additionally, horse chromosomes contain genetic content similar to that of human chromosomes, making them relevant for research on chromosomal anomalies.

Determining the causes of early miscarriage in humans has been challenging due to the loss of most fetuses during this period at home, which leaves scientists without necessary material and data for study.

This research provides crucial insights into the frequency of chromosomal errors during the equivalent of the first six weeks of human gestation.

Horses, often highly valued and receiving extensive care, provide a wealth of data through routine pregnancy tracking, unlike other animal models such as mice.

Mice, with a gestation period of about three weeks and a low rate of natural pregnancy loss, are not comparable to human pregnancies.

Genetic causes of pregnancy loss

The study’s findings have practical implications for equine health, particularly in the clinical management of pregnancies. For instance, if a significant chromosomal error is detected, clinicians might reconsider using hormones to prolong the pregnancy, a common practice in managing pregnant mares.

The research also paves the way for developing new diagnostic tests for chromosomal abnormalities in horse fetuses and further investigation into the molecular mechanisms behind these abnormalities.

“This research has provided a foundation for understanding the genetic causes of pregnancy loss in horses, often referred to as pregnancy loss of unknown cause,” said Shebl Salem, a postdoctoral researcher in de Mestre’s Equine Pregnancy Lab and co-first author of the study.

The study not only enhances the understanding of equine pregnancy but also offers valuable insights into human reproductive health, highlighting the potential for horses to serve as a key model in studying pregnancy loss due to chromosomal abnormalities.