Dystocia is a term referring to the inability to expel a fetus during the birthing process. Dystocia may occur for a variety of reasons including functional (uterine inertia) or obstruction (maternal-fetal disproportion, malpositioned fetus, fetal malformations, etc). The most common cause of dystocia in cats is uterine inertia, however all the above causes are possible. Dystocia is a life threatening medical emergency that, if not treated, may lead to death of both mother and kittens. While dystocia is less common in cats than in other species, there has been an association described with both very large and very small litter sizes.
In dogs, an increased risk of dystocia has been described in certain breeds. To date, no such correlation has been described in cats. The purpose of this study was to determine if there is a breed predisposition towards dystocia in felines. The study was designed as a retrospective review of medical records from a Swedish insurance database. Data were collected from reimbursement and life insurance claims from 1999 to 2006 with the Agria Pet Insurance company.
41 breed codes were used by the insurance database. For this study, similar or related breeds were grouped together for the purposes of analysis; for example, Abyssinians and Somalis, Persian and Exotic Shorthair, and Oriental breeds. Records were evaluated for claims related to dystocia or cesarean section. Only female cats were evaluated. European Shorthairs were excluded from the study due to concerns for misclassification. Bengal, Sphynx, and Siberian were also excluded as they were relatively new entrants to the breed registry and authors were concerned that the number of breeding females would be disproportionately high.
Data was analyzed based on the number of cases per Cat-Year at Risk (CYAR). From 1999-2006 there were 133 631 cats enrolled with veterinary insurance, for a total of 438 558 CYAR. In this population, there was an average of 22 events per 10 000 CYAR. The incidence was 67/10 000 CYAR for purebred cats, compared with 7/10 000 CYAR for domestic cats. The incidence risk ratio (IRR) for purebred vs domestic was 9.3. 56% of cats with dystocia underwent cesarean section.
Of the 670 cats who had both life insurance and veterinary insurance, 670 cats had a claim for dystocia of which 13 had a life insurance claim, for a case fatality rate of 2%. The overall rate of dystocia in purebred cats was similar to what has been previously reported in dogs.
The highest IRRs were found for British Shorthairs and Oriental breeds. The lowest IRRs were present in Maine Coons and Norwegian Forrest Cats.
The lower risk of dystocia in domestic cats compared to purebreds or in certain breeds compared to others does not necessarily imply a predisposition to dystocia. Only pregnant cats are at risk for dystocia, and as the rate of pregnancy was not known, a proper denominator was not determined for this study. Domestic cats are more likely to be neutered and less likely to be enrolled in a breeding program, and so less likely to be at risk for dystocia. Certain breeds may have more active breeding programs than others.
The authors hypothesize several possible causes for differences in dystocia rate between breeds. These include body confirmation, average litter size, selection for good birthing characteristics, and others. Interestingly, a correlation between dystocia and brachycephalic breeds was not seen in this study, unlike documented trends in dogs. The Siamese/Exotic group in particular had a remarkably low rate of dystocia, which may be in part due to the very small breeding population in Sweden.
There were several drawbacks to this study, including an inability to properly determine a denominator for events, the bias inherent in looking only at insured cats, and the ability to extrapolate Swedish data to other countries. The exclusion of several popular modern breeds (such as Sphinx and Bengal) also limits the relevance of some data. Overall, this paper does provide a good overview of approximate rates of dystocia in cats, and of the relative risks in certain breeds. This information is valuable not only to veterinarians, but to breeders who may wish to reduce the risks of this complication of pregnancy.