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

Abstract

SummaryA 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.