Abortion Due to Umbilical Torsion in a Mare
By Drs. Jason Grady and Mike Moore
Abortion due to umbilical torsion ranges from 2.4-6.0% in studies in the United States, to 35.7% in a study in the United Kingdom. The causes of umbilical torsion are not completely understood. However cords from torsion cases average greater than 85 cm in length. Most abortions due to umbilical cord torsion occur in months 6-8 of gestation. Mobility is highest in months 4-7 of gestation, providing the greatest opportunity. Pregnancies where the gravid horn was opposite the horn of implantation may be correlated with longer umbilical cords. Other potential contributing factors include increased fetal activity, excessive fetal fluids and uterine dimensions. Careful examination of the expelled fetal membranes must be performed since twisting of the umbilicus alone does not confirm a diagnosis.
History: An aborted male Arabian foal (9 months gestation) was submitted for an abortion workup. The mare aborted shortly after being moved to a new location. She had received EHV-1 vaccines at 5, 7, and 9 months of pregnancy.
Diagnostics: The umbilical cord was 124.5 cm long and had approximately 20 twists. (Figure 1) There was moderate congestion and edema of the umbilicus. (Figure 2) Histopathology of the umbilical cord revealed diffuse congestion of the smaller blood vessels in the adventitia and whartons jelly of the umbilicus, and the adventitia contained clear spaces separating the interstitial collagen bundles (edema).(Figure 3) Bacterial culture was performed on lung, liver, stomach contents and the placenta. There was no significant growth. Lepto PCR was negative. Virus isolation was negative. Equine Herpesvirus type 1 and Equine Viral Arteritis serology was performed and was also negative.
Diagnosis: Abortion due to umbilical torsion, and hypertrophy.
Take home messages from this case: Normal fetal mobility during pregnancy often results in twisting of the umbilical cord without any risk to the pregnancy. It has been reported that 78% of normal umbilical cords have an average of 4.4 twists per cord. Gross findings supporting a diagnosis of umbilical torsion include umbilical vessel constriction, thrombosis or aneurysms, local hemorrhage into the wall of the cord, and kinking of the cord after unwinding the umbilical cord. When the fetus is expelled it is typically autolyzed indicating death prior to abortion. Other common causes of late term abortion in mares include placentitis, EHV-1 (and less commonly EHV-4) induced abortion, twinning, Equine Viral Arteritis, and illness of the mare. At this time umbilical torsion appears sporadic with no apparent increased risk for future problems in mares that loose a foal due to this condition.
When faced with an abortion, thorough examination of the fetus and fetal membranes is critical. Submission of the fetus and placenta along with serum from the mare will provide the best chance of achieving a diagnosis. Submission of the entire fetus and placenta may be performed in a clean garbage bag and delivered in a Styrofoam cooler on ice packs at 35-40⁰F. A post-mortem exam may also be performed and appropriate tissues submitted. Do not freeze the tissues, and the submission should arrive the day of or by overnight submission. Samples of the gravid horn, nongravid horn, cervical star, body of the placenta, umbilicus, and amnion should be submitted for aerobic culture and histology. Submission of fetal tissues for aerobic culture commonly include fetal lung, stomach contents, and liver. Histology and PCR is commonly performed on adrenal glands, brain, heart, liver, lung, small intestines, spleen, and any other tissues that may appear abnormal.