Dystocia and Obstetric Crises

Chapter 140 Dystocia and Obstetric Crises



Michelle Kutzler, DVM, PhD, DACT



KEY POINTS



• Knowledge of actual length of gestation and timing of normal events during parturition are critical when managing dystocia.

• Primary uterine inertia is the most common cause of dystocia in dogs and cats.

• Diagnosis of dystocia can be made from the history and physical signs. However, diagnosing the cause of dystocia may require biochemical testing, vaginal palpation, radiographic and/or ultrasonographic imaging, and uterine contractility monitoring.

• If obstructive causes of dystocia have been ruled out, oxytocin administration may be employed provided that fetal heart rates are normal. Subcutaneous or intramuscular oxytocin (0.25 to 2.0 IU per bitch or queen initially; maximum administered dose of 4 IU) induces uterine contractility lasting for 30 to 90 minutes.

• Sequelae of dystocia include neonatal and maternal mortality, retained placenta, uterine prolapse, and perineal-vaginal fistula formation.


NORMAL PARTURITION


Knowledge of actual length of gestation is critical when managing dystocia. Female cats are seasonally polyestrous, with ovulation occurring 24 to 48 hours after breeding. The interval from ovulation to parturition is 63 to 65 days.1 The apparent length of gestation in the dog ranges from 58 to 72 days from the first of multiple breedings because of the variability in the onset of estrous behavior, prolonged viability of sperm in the uterus, and prolonged life span of the oocytes. Predicting parturition date in the bitch is straightforward if ovulation timing has been performed, because length of gestation is 56 to 58 days from the onset of cytologic diestrus or 64 to 66 days from the surge in luteinizing hormone. The most definite indication of impending parturition is a sudden drop in body temperature that occurs with prepartum luteolysis (decline in progesterone). Rectal temperature decreases by at least 2° F (1° C) 12 to 24 hours before the onset of parturition. However, the hypothermia is transient and body temperature rises during parturition, remaining slightly above normal for several days.


The first stage of labor is characterized by intermittent uterine contractions associated with cervical dilation, vaginal relaxation, and behavioral changes (restlessness, panting, and nesting). In the bitch, the first stage of labor lasts 6 to 12 hours. Uterine contractions that occur during this stage are not visible externally and are not accompanied by voluntary abdominal contractions.


The second stage of labor is characterized by intensified uterine contractions accompanied by voluntary abdominal efforts, resulting in fetal expulsion. In the bitch, the second stage of labor lasts for 3 to 12 hours and, in rare cases, up to 24 hours depending on litter size and without obvious complications.2–4 Canine litter size ranges from 1 to 23 pups, with mean litter sizes ranging from 4 to 8 depending on breed (up to 10 pups in Bloodhounds and fewer than 3 pups in Pekingese and Pomeranians).5 Average feline litter size is 3 to 4 kittens.1


Approximately 60% of canine and feline fetuses are delivered in cranial presentation, with the remainder delivered in caudal presentation. Fetuses typically are covered by the amnion at the time of delivery.3 Delivery is initiated from the uterine horn carrying the most fetuses unless they are evenly distributed between the uterine horns; then they are delivered alternately from the two horns.3 Expulsion of the first fetus may take up to an hour,2 usually within 15 minutes from the onset of forceful straining.3 Survival of the first fetus after initiation of second stage labor is estimated to be 6 to 8 hours, but little is known about canine and feline fetal intrapartum survival if dystocia occurs.


The interval between delivery of individual fetuses ranges from 5 minutes to 2 hours.3,4,6 When more than 2 hours elapses between consecutive births, fetal survival is thought to be endangered. Intrapartum uterine contractions occur mainly at the level of the uterus around the fetus closest to the cervix, which may explain the birth of normal fetuses even with prolonged intervals between delivery. It is important to note that stressed bitches can postpone the delivery of pups for up to 1 day without complications,7 although such postponement generally applies to onset of parturition rather than a prolongation of the interpup interval.8 During dystocia, excessive and prolonged straining may result in premature placental separation and fetal mortality. However, in the absence of straining, the risk of intrapartum fetal death may not be increased.8


Throughout and following parturition, dark green uterine discharge (uteroverdin) originating from the uteroplacental marginal hematomas is present in bitches. The third stage of labor is characterized by placental expulsion and uterine involution. Placentas are delivered 5 to 10 minutes following delivery of the fetuses. Two to three fetuses may be delivered before their placentas are passed.3 The physiology of placental detachment is not well understood in cats and dogs. However, placental aging and detachment can occur even in the presence of high progesterone concentrations, suggesting that the placenta has a predetermined life span that cannot be prolonged with progestin supplementation.9



ETIOLOGY AND INCIDENCE


Dystocia comes from the Greek dys (difficult) and tokos (birth). Dystocia can be classified as functional or obstructive. Functional dystocia usually is termed inertia and can be classified as primary or secondary. Primary uterine inertia is the most common cause of dystocia in dogs and cats, with a reported incidence of up to 91% of cases.4,10,11 In primary uterine inertia, the myometrium produces weak, infrequent contractions resulting in a failure to deliver the fetuses. Primary uterine inertia can be further classified as complete or partial.12 In complete primary inertia, second stage labor does not start; whereas in partial primary inertia, second-stage labor starts but labor ends prematurely in the absence of obstructive causes.


Secondary uterine inertia occurs following a prolonged second stage of labor and may be associated with obstructive dystocia. Obstructive dystocia may result from relative or absolute fetal oversize. Absolute fetal oversize refers to a fetus that is too large to pass along a maternal birth canal that is of normal dimensions. Relative fetal oversize refers to a fetus of normal size that cannot pass along the maternal birth canal because the latter is abnormally small or restricted in some way. Relative fetal oversize is equivalent to a maternal obstructive dystocia. Known and speculated etiologies for both functional and obstructive dystocia are listed in Box 140-1.



Box 140-1 Causes of Functional and Obstructive Dystocia in Dogs and Cats



Primary Uterine Inertia



Age

Absence of fetal fluid
Dietary deficiencies

• Hypocalcemia

• Hypoglycemia

• Hypomagnesemia

Environmental disturbance
• Stressed

• Unfamiliar surroundings

Large litter size
• Excessive uterine distention

• Overstretching

Myometrial defect
• Hereditary

• Infection

Obesity
• Fatty myometrial infiltration

Oxytocin deficiency

Small litter size
• Insufficient fetal cortisol

Systemic illness


Secondary Uterine Inertia



Diaphragmatic rupture

Excessive pain

Muscle fatigue

Obstructive dystocia

Perforated trachea

Uterine rupture


Maternal Obstructive Dystocia



Aberrant round ligaments encircling the uterine horn

Related posts:

  1. Deteriorating Mental Status
  2. Hyperthermia and Fever
  3. Ventilator-Associated Lung Injury
  4. Allergic Airway Disease in Dogs and Cats and Feline Bronchopulmonary Disease

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Sep 10, 2016 | Posted by in SMALL ANIMAL | Comments Off on Dystocia and Obstetric Crises

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