Large placental area of degeneration in a twin pregnancy in a mare (Equus caballus)

Abstract

Summary A primiparous mare foaled a live foal and a mummy. The mummy and its fetal membranes were necrotic and had been invaginated within the fetal membranes of the live foal. Near the mummy, the fetal membranes of the live foal had a clear demarcation between a ‘white’ and a ‘red’ region. The white region was touching the mummy, and some of its features were similar to those of a fetal–foot placental area of degeneration (PAD): it was ischaemic and degenerate (as indicated by hypoplasia, hyaline degeneration, multifocal squamous metaplasia, cell swelling and basement membrane sclerosis) with villi that were shorter than normal and limited in number. However, the PAD in this case was thinner than those in previous reports, and it was much larger, as it surrounded the entire mummy. The red region, which was touching the maternal endometrium, was hyperaemic, but in other respects, it was similar to the fetal membranes in the other uterine horn. To the authors’ knowledge, this is the first extensive report on the histology of type C twinning (i.e. with a mummified foal) in which the death of one foal had not been induced.

Love thy neighbour – unless they are sharing your uterus

“…From the Type C twin placentation described by Rapacz‐Leonard and Paździor‐Czapula (2022), in the present issue, to the increasing appearance of reports mentioning monochorionic twin placentation in the horse, such anomalies are both intriguing and worthy of discussion to better understand the tribulations of the fetus in utero . They also provide a timely reminder that there is no room for complacency when undertaking ultrasound pregnancy examinations in the mare as there is always the possibility of a twin pregnancy, even when only a single ovulation has been noted, or a single in vivo derived or IVP embryo has been transferred to a recipient mare.…”

“…The Case Report in this issue entitled ‘Large placental area of degeneration in a twin pregnancy in a mare ( Equus caballus )’ (Rapacz‐Leonard and Paździor‐Czapula 2022) illustrates the case of a co‐twin surviving to term along with its mummified sibling. The twin placentation described in this case is Type C where one twin undergoes mummification and occupies on average only 15% of the uterus whilst the other twin occupies the remaining 85% encompassing all of one uterine horn, the body and part of the other uterine horn with the fetal membranes of the mummified twin enveloped in a large invagination (Jeffcott and Whitwell 1973).…”