School of Veterinary and Animal Science, Federal University of Goiás, Goiânia, Goiás, Brazil
Dystocia (Greek dys = difficult, tokos = birth) is defined as the inability to expel fetuses through the birth canal during parturition and may result from maternal or fetal factors that prevent delivery from taking place.1 Dystocia occurs in approximately 5% of all parturitions in dogs2 and 3.3%3 to 5.8%4 of parturitions in queens. In relation to maternal causes, can mentioned physiologic and morphologic causes. Fetal factors that may result in dystocia include malpresentations, oversize, fetal malformations, and fetal death.4,5
1.1. Maternal Causes Physiologic
1.1.1. Uterine Inertia
Uterine inertia is the most common cause of dystocia, seen when the myometrium produces only weak and infrequent contractions that fail to expel a normal fetus through a normal birth canal. Uterine inertia may be considered primary when gestation has exceeded its expected length with no evidence of progression into active labor and secondary if myometrial failure results from prolonged attempts to expel an obstructed fetus and persists after relief of obstruction.5
1.1.2. Other Physiologic Causes
Hereditary, stress/environmental disturbances, old age, obesity, systemic disease, uterine overdistention (large litter size or fetuses too big), uterine underdistention (small litter size, inadequate, fetal fluids), estrogen/progesterone balance, calcium/magnesium balance, inadequate oxytocin secretion, prematurity.1
1.2. Maternal Causes Morphologic
Morphologic causes of dystocia are those in which an anatomic abnormality of the bitch or queen results in obstruction of the birth canal. Primary morphologic abnormalities are commonly seen in narrow-hipped dogs like Bulldogs, Boston Terriers, and Scottish Terriers, where the birth canal is too small to allow passage of a fetus that is considered to be of normal size for the breed.6 Secondary morphologic causes of dystocia result from an abnormal influence on or within the birth canal (pelvic fractures) that leads to obstruction.1
1.3. Fetal Causes
Malpresentations are reported to be the second most common cause of dystocia in dogs and cats.4,5 The faulty foetal presentations most commun are transverse presentation and simultaneous presentation of two foetuses. The faulty foetal posture most commun are lateral deviation of the head and ventral deviation of the head. If a foetal malformation such as anasarca, schistosoma reflexum, hydrocephalus or conjoined twins is present, the foetus usually is too large for the birth canal and has to be delivered surgically. Dead foetuses may occasionally cause an obstructive dystocia, especially if the first foetus to be delivered is dead or if massive emphysema formation has already taken place.7
A number of breeds have been reported to have a higher prevalence of dystocia. Congenitally narrowed birth canals are seen in many brachycephalic and terrier breeds, such as Bulldogs, Boston Terriers, and Scottish Terriers, and their fetuses may have comparatively large heads, predisposing them to maternal-fetal disproportion.6
Bulldogs also tend to have slack abdominal musculature that may limit their ability to lift the fetus up toward the birth canal. Many of the small and toy breeds have also been overrepresented in retrospective studies, including Chihuahuas, Pekinese, Yorkshire Terriers, Dachshunds, and Poodles.8 In feline dystocia, breed and cranial conformation have also been significantly associated with dystocia, with Siamese and Persians heavily overrepresented. In one study looking at the association between cranial conformation and dystocia, the prevalence of dystocia was 10% in dolichocephalic breeds (e.g., Siamese, Cornish Rex), 7.3% in brachycephalic breeds (e.g., Persian, British Shorthair), and only 2.3% in mesocephalic cats.4
2. Treatment of Dystocia
When dystocia is diagnosed in the bitch or queen, two forms of treatment exist: medical or surgical therapy.
2.1. Medical Agents Used in the Treatment of Dystocia
Medical management of dystocia has the advantage of aiding completion of the parturition process without surgery or anesthesia.
Oxytocin is a nine amino acid peptide hormone that is produced endogenously by hypothalamic neurons. Oxytocin is also produced by the large luteal cells of the corpus luteum and is involved in luteolysis.9 When oxytocin has been used alone, doses have historically been reported as high as 5–20 UI administered IM in the dog, and 2–4 UI administered IM in the cat.1
2.1.2. Calcium Gluconate
Contraction of skeletal, cardiac, and smooth muscle cells (e.g., myometrium) results from the sliding together of actin and myosin protein filaments. Calcium therapy is described for queens, but is used less frequently. Dosages reported include 0.5–1.0 ml per cat IV1. Calcium use in the queen is controversial, because of the very strong uterine contractions exhibited after administration.9
Some authors have proposed hypoglycemia as a cause of primary inertia, especially in toy breeds of dogs.2 Others report that hypoglycemia is uncommon in canine dystocia. Regardless, blood glucose is something that can be rapidly measured in most veterinary hospitals to determine if hypoglycemia is present and requires treatment.9
2.2. Surgical Management of Canine and Feline Dystocia
If medical management of dystocia has failed or is inadvisable, a cesarean section is indicated. The necessity of surgery is primarily based on the condition of the dam, progression of labor, and fetal heart rate. Timely intervention is crucial for optimal fetal and maternal survival. Surgical technique may vary, based on the needs of each individual case. There are many options for each portion of the surgery, including the choice of anesthetic protocol, abdominal approach, uterine incision location, and post-surgical pain management. The episiotomy is rarely used to treat dystocia.10
Know the main causes of dystocia in dogs and cats and their treatments can increase the life expectancy of animals involved.
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2. Linde-Forsberg C, Eneroth A, Ettinger SJ, Feldman EC, eds. Abnormalities in Pregnancy, Parturition, and the Periparturient Period. WB Saunders, Co. 2000;1527–1538.
3. Humphreys J. Dystocia in cats. Vet Rec. 1974;(95):353.
4. Gunn-Moore DA, Thrusfield MV. Feline dystocia: prevalence and association with cranial conformation and breed. Vet Rec. 1995;(136):350–353.
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6. Cruz R, Alvarado MS, Sandoval JE, et al. Prenatal sonographic diagnosis of fetal death and hydranencephaly in two Chihuahua fetuses. Vet Radiol Ultrasound. 2003;(44):589–592.
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8. Gaudet DA. Retrospective study of 128 cases of canine dystocia. J Am Anim Hosp Assoc. 1985;(21):813–818.
9. Pretzer SD. Medical management of canine and feline dystocia. Theriogenology. 2008;70(3):332–336.
10. Traas AM. Surgical management of canine and feline dystocia. Theriogenology. 2008;70(3):337–342.