Umbilical cord torsion abortion: the gross and histological features of affected umbilical cords and fetal membranes.

Umbilical cord torsion (UCT) is the most frequent pathology of the equine umbilical cord (UC) and a prominent cause of abortion, yet objective data on its features remain limited. This study compared UCT with clinically normal pregnancies (CNP) to (i) identify gross and histological features of the UC and fetal membranes, (ii) determine whether UCT is associated with fetal growth restriction, and (iii) rule out infectious aetiologies. Gross and histological features of the UC, chorioallantois and amnion were compared between groups. Fetal weight and crown-rump length were analysed relative to gestational age. Inflammatory infiltrates were evaluated and PCR screened chorioallantoic tissue for equine herpesviruses, Chlamydia psittaci, Coxiella burnetii and Leptospira spp. Alternating reddening and blanching on the amniotic UC was observed in all UCT cases and absent from CNP (p < 0.001). Less specific, yet significant, features included amniotic UC stretch marks, membrane congestion, increased visibility of UC stromal vasculature, villous mineralisation, and karyorrhexis. The UCT cords were longer (total length 81.1 cm 95 % CI 77.7-84.6 vs. 54.2 cm 95 % CI 49.5-59.0, p < 0.001), with a larger intraamniotic portion (p = 0.04). Fetal weight did not differ significantly between groups (p = 0.08), but crown-rump length was reduced in UCT (p = 0.01). No significant inflammatory infiltrates were detected, and all screened samples tested negative for equine herpesviruses, C. burnetii and C. psittaci. This study defines UCT by reproducible gross and histological features and introduces a diagnostic matrix for improved assessment of risk factors and mechanisms of UCT abortion.