Telephone enquiries regarding possible cases of dystocia are relatively common in companion animal emergency practice. Owners are often anxious and distressed at these times and veterinary staff must have a good understanding of normal gestation and parturition in order to provide sound logical advice.
Normal gestation and parturition
Average length is 65 days (range 56–72 days). This range reflects the variable correlation between copulation and actual fertilization in the bitch. Once fertilization actually occurs, the true gestation length is less variable.
Labour is divided into three stages.
Stage one occurs 24–48 hours before parturition. Behavioural changes may include:
Stage two occurs 3–24 hours before parturition. There are three cardinal signs indicating that the dam is in stage two although all three signs may not be present in any individual case.
A green vulval discharge is normal in the bitch as long as it is produced less than 2 hours before, with, or after foetal delivery. This discharge is due to placental separation. Following delivery the dam should remove the amniotic membranes, sever the umbilical cord, and clean and bond with the foetus.
Stage three represents expulsion of placental and foetal membranes and occurs concurrently with stage two in pluriparous dams. Expulsion usually occurs within 15 minutes of delivery but the dam may deliver two or more foetuses before any membranes are expelled. Maternal consumption of the membranes may induce gastrointestinal signs and should be discouraged. Discharge of residual foetal fluids and placental remains may persist for 3–6 weeks after parturition has ended. However failure to pass the majority of all placentas within 4–6 hours of the end of second stage labour should prompt veterinary attention.
Gestation and parturition in the queen are similar to the bitch with a few noteworthy exceptions.
The incidence of dystocia in dogs and cats is reported to be approximately 5% and dog breeds that may be at increased risk include chondrodysplastic and brachycephalic breeds, especially Pugs and Bulldogs, as well as Scottish terriers, Boston terriers, Yorkshire terriers and the Chihuahua. Dystocia is most common in short-faced breeds as well as Devon Rex and Siamese cats. Primary uterine inertia is the most common cause of dystocia in dogs and cats and is a maternal cause. Other maternal causes include mechanical obstruction (e.g. due to narrowing of the pelvic canal secondary to healed fractures), maternal anxiety and systemic illness. Foetal malpresentation is the most common foetal cause of dystocia in dogs and cats. Others include foetal oversize, malformation and death.
BOX 37.1 Indications for veterinary attention during parturition
Note that posterior presentation is considered to be a normal variation in dogs and cats.
Oxytocin is a hormone that is released during labour and that causes uterine smooth muscle contraction as well as milk letdown. It is used to treat dystocia due to uterine inertia by increasing the frequency and strength of uterine contractions which it does by promoting calcium influx into myometrial cells. Oxytocin also promotes uterine involution after birth as well as reducing uterine haemorrhage and assisting in expulsion of retained placentas.