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

Overview

• This study investigates the features of umbilical cord torsion (UCT), a common cause of abortion in horses, by comparing affected cases to normal pregnancies.
• The research identifies specific gross and microscopic signs of UCT, evaluates fetal growth, and excludes certain infections as causes.

Background and Purpose

• Umbilical Cord Torsion (UCT): The twisting of the umbilical cord in horses, which is a frequent pathology leading to abortion.
• Despite being common, objective data detailing the characteristics of UCT in terms of gross anatomy and histology have been limited prior to this study.
• The study aims to:
  • Identify the gross (visible) and histological (microscopic) features of the umbilical cord (UC) and fetal membranes affected by UCT.
  • Determine if UCT is associated with fetal growth restriction.
  • Exclude infectious agents as contributing causes by screening for specific pathogens.

Methods

• Comparison groups included:
  • Equine pregnancies affected by UCT.
  • Clinically normal pregnancies (CNP) serving as controls.
• Examination of samples involved:
  • Gross examination of UC and fetal membranes, including chorioallantois and amnion.
  • Histological evaluation for microscopic features.
  • Measuring fetal weight and crown-rump length relative to gestational age to assess growth restriction.
  • Evaluating inflammatory cell infiltrates under microscopic examination.
  • Molecular testing (PCR) of chorioallantoic tissue for presence of equine herpesviruses, Chlamydia psittaci, Coxiella burnetii, and Leptospira species to rule out infection.

Key Findings

• Gross Features Specific to UCT:
  • Alternating reddening and blanching (discoloration) on the amniotic portion of the umbilical cord was observed consistently in all UCT cases, and was absent in normal pregnancies (statistically significant, p < 0.001).
  • Other notable but less specific features included:
    • Stretch marks on the amniotic umbilical cord.
    • Congestion of fetal membranes.
    • Increased visibility of stromal blood vessels within the umbilical cord.
    • Presence of mineral deposits (villous mineralisation) and nuclear debris (karyorrhexis) in microscopic samples.
• Umbilical Cord Morphology:
  • UCT cords were significantly longer than those from normal pregnancies (average 81.1 cm versus 54.2 cm, p < 0.001).
  • The intraamniotic segment (the part within the amnion) of the UC was also longer in UCT cases (p = 0.04).
• Fetal Growth Parameters:
  • Fetal weight did not differ significantly between affected and control groups (p = 0.08), indicating no clear fetal growth restriction based on weight.
  • However, crown-rump length—a linear measurement used to assess fetal size—was significantly reduced in UCT cases (p = 0.01), suggesting some degree of growth impairment.
• Inflammatory and Infectious Evaluation:
  • No significant inflammatory cell infiltration was identified in the UC or fetal membranes of UCT cases.
  • Molecular testing for infectious agents (equine herpesviruses, Chlamydia psittaci, Coxiella burnetii, Leptospira spp.) was negative in all samples, effectively ruling out these infections as causes of the abortions.

Conclusions and Implications

• The study establishes reproducible gross and histological features that define umbilical cord torsion in horses, improving the ability to diagnose this condition objectively.
• A diagnostic matrix derived from these features helps in assessing risk factors and understanding the mechanism behind UCT-induced abortion.
• Knowledge gained can enhance veterinary diagnostic accuracy and inform management or prevention strategies for equine pregnancy loss linked to UCT.
• The absence of infection as a contributing factor clarifies that UCT is primarily a mechanical and pathological condition rather than an infectious one in the populations studied.