Problems of pregnancy and parturition (Proceedings)
Dystocia, or difficult birth, has an overall prevalence of approximately 5% to 6% of pregnancies in bitches and queens. In certain breeds, however, the prevalence is much higher, approaching 18% in Devon Rex cats in the United Kingdom and 100% in English Bulldogs in the United States. It is a major cause of neonatal mortality in puppies and kittens. Overall mortality rates from birth to weaning average 12% (range 10% to 30%) in puppies and 13 % in kittens, but 65% of those losses occur at parturition and during the first week of life as a result of stillbirth, fetal stress, and hypoxia related to parturition.
The two most common causes of dystocia in small animals are (1) uterine inertia and (2) fetal malpresentation. Of these, uterine inertia is by far the most common, accounting for about 60% of all cases. Uterine inertia is the failure to develop and maintain uterine contractions sufficient for normal progression of labor. Uterine inertia has a variety of potential causes (e.g., genetic, age, nutrition, metabolic) but the specific cause for a particular case usually is not identified. The exception is mechanical obstruction that results in myometrial exhaustion and secondary uterine inertia. Fetal malpresentation accounts for approximately 15% of dystocia cases in bitches and queens.
Maternal causes of obstructive dystocia relate primarily to abnormalities in size or shape of the pelvic canal. Cephalo-pelvic disproportion, in which the fetal head is too large for the small maternal pelvic canal, also can occur. Uterine torsion is also a cause of obstruction. Malpresentation is the most common fetal cause of obstruction. Fetal oversize or congenital deformities causing large abnormal shape may also cause obstruction. Small litter size predisposes to dystocia in bitches for a variety of reasons. The fetal signals that initiate parturition may be insufficient in very small litters. This may lead to prolonged gestation. A negative correlation between litter size and puppy size exists: the smaller the litter, the larger the individual pup. This may increase the likelihood of obstruction. Conversely, a very large litter may overstretch the uterus and lead to inertia. Litter size has no apparent bearing on the occurrence of dystocia in queens. Fetal death accounts for 1% to 4.5% of dystocia in bitches and queens, respectively. Extreme anxiety reportedly inhibits normal progression of labor.Early recognition and correction of dystocia is crucial to the successful management and optimal neonatal health. The first things that should be determined are the presence of placental membranes or fetal parts at the vulva, and the presence and character of any vulvar discharge. A partially delivered puppy or kitten needs immediate attention. Breeders should be asked if they have already administered any drugs or performed any obstetric procedures. The following historical findings are indicators of dystocia and reason to recommend that the animal be examined:
A common error made by owners and veterinarians is to delay intervention based on the fact that the dam does not appear to "be in trouble." The fetuses are often severely stressed long before the dam shows clinical signs relating to their demise. The dam should be examined and ultrasound performed to assess fetal viability if the expected due date has arrived and no signs of labor exist, irrespective of a lack of maternal discomfort or illness.