Dystocia

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Dystocia

 

Dystocia is difficult birth.

 

PATHOPHYSIOLOGY

Dystocia may occur as a result of maternal or fetal factors and may occur during any stage of labor.

Abnormal presentation, posture, and position; may be causal. Normal: anterior or posterior longitudinal, dorsosacral, and head and feet extended.

 

Three stages of labor:

Stage 1

Early onset of uterine contractions and relaxation of the cervix; ends with rupture of first chorioallantoic sac—averages 6–12 h (up to 36 h in nervous, primiparous bitch).

Bitch—may be restless, nervous, shiver, pant, pace, and nest.

Queen—tend to vocalize initially; purr and socialize as Stage 1 progresses.

 

Stage 2

Delivery of the fetuses.

Bitch—obvious abdominal contractions; from beginning of stage 2 to delivery of first offspring usually < 4 h; time between delivery of subsequent fetus usually 20–60 min (may be as long as 2–3 h).

Queen—average length of parturition is 16 h, with a range of 4–42 h (up to 3 d in some cases may be normal); important to consider this variability when intervening.

Number of fetuses present may significantly affect the length of stages 2 and 3.

 

Stage 3

Delivery of the fetal membranes.

May alternate between stage 2 and 3 with multiple fetuses.

 

INCIDENCE/PREVALENCE

Dog: incidence unknown; difficult to estimate due to breed variability and breeder intervention.

Cat: reported average ranges from 3.3–5.8%; mixed-breed cats 0.4%; increased with pedigreed cats, to a high of 18.2% in the Devon rex.

 

SIGNALMENT

Breed Predilections

Dogs

Higher incidence with miniature and small breeds due to small litter size with concurrent large fetal size; may occur in large breeds with large or singleton litters.

Brachycephalic—broad head and narrow pelvis—Bulldog, Boston terrier, pug.

Large fetal head: maternal pelvis ratio—Sealyham terrier, Scottish terrier.

Uterine inertia—Scottish terrier, dachshund, border terrier, Aberdeen terrier, Labrador retriever (see Uterine Inertia).

Miscellaneous breeds with overall increased incidence of dystocia—Chihuahua, dachshund, Pekingese, Yorkshire terrier, miniature poodle, Pomeranian.

 

Cats

Brachycephalic—Persian, Himalayan

Dolichocephalic—Devon rex

 

SIGNS

Historical Findings

  • Indicators of dystocia include:
  • More than 30 min of persistent, strong, abdominal contractions without fetal delivery.
  • More than 4 h from the onset of stage 2 to delivery of first fetus (bitches).
  • More than 2 h between delivery of fetuses (bitch).
  • Failure to commence labor within 24 h of the drop in rectal temperature below 37.2°C (99°F) or within 36 h of serum progesterone < 2 ng/mL (bitch).
  • Female cries, displays signs of pain, and constantly licks the vulvar area when contracting.
  • Prolonged gestation—more than 72 d from day of first mating (bitch); more than 59 d from the first day of cytologic diestrus (bitch); more than 66 d from LH peak (bitch); more than 68 d from the day of mating (queen).

 

Physical Examination Findings

  • Presence of greenish-black discharge (uteroverdin) preceding the birth of first fetus by more than 2 h.
  • Presence of bloody discharge prior to delivery of first fetus.
  • Diminished or absent Ferguson’s reflex (stimulation or pressure to dorsal vaginal wall to elicit abdominal straining: “feathering”) indicates uterine inertia.

 

CAUSES

Fetal

  • Oversize; fetal monsters, fetal anasarca; fetal hydrocephalus; prolonged gestation due to inability of a singleton fetus to initiate labor.
  • Abnormal presentation, position, or posture of fetus in the birth canal.
  • Fetal death.

 

Maternal

  • Inadequate uterine contractions (primary or secondary uterine inertia)—myometrial defect; biochemical imbalance; psychogenic disturbance; exhaustion.
  • Ineffective abdominal press—pain; fear; debility (exhaustion); diaphragmatic hernia; age.
  • Placentitis, metritis, endometritis.
  • Pregnancy toxemia, gestational diabetes.
  • Abnormal pelvic canal—previous pelvic injury; abnormal conformation; pelvic immaturity.
  • Congenitally small pelvis—Welsh corgis; brachycephalic breeds.
  • Inguinal hernia.
  • Abnormality of the vaginal vault—stricture; septae; vaginal hyperplasia; hypoplastic vagina; intraluminal or extraluminal cysts; neoplasia.
  • Abnormality of the vulvar opening—stricture; small vulva; fibrosis from trauma; neoplasia.
  • Insufficient cervical dilation.
  • Lack of adequate lubrication.
  • Uterine torsion.
  • Uterine rupture.
  • Uterine neoplasia, cysts, or adhesions.

 

RISK FACTORS

  • Age
  • Brachycephalic and toy breeds
  • Persian, Himalayan, and Devon rex breeds
  • Obesity
  • Abrupt changes in environment peripartum
  • Previous history of dystocia

 

DIAGNOSIS

DIFFERENTIAL DIAGNOSIS

Uterine inertia—hypocalcemia versus hypoglycemia

 

PHYSICAL EXAMINATION

  • Complete physical examination—determine concurrent or contributing problems (e.g., hypoglycemia, hypocalcemia, dehydration, fever); perform careful abdominal palpation to confirm the existence of fetuses.
  • Digital vaginal examination—presence of a fetus or fetal membranes in the vaginal canal; abnormalities of the maternal pelvic canal; assess Ferguson’s reflex.
  • Bitches unresponsive to oxytocin or lacking Ferguson’s reflex—uterine inertia more likely than obstructive dystocia, except if obstructed for several hours.

 

CBC/BIOCHEMISTRY/URINALYSIS

Minimum database—PCV, total protein, BUN, serum glucose, and calcium concentrations (ionized preferable to total serum calcium).

 

OTHER LABORATORY TESTS

Progesterone concentration

 

IMAGING

Radiography—determine pelvic conformation, number and position of fetuses, evidence of fetal obstruction, fetal oversize, and fetal death; may require two views.

Radiographic evidence of fetal death—collapse of fetal skeletons, abnormal association of fetal bones to the axial skeleton, presence of air/gas surrounding a fetus, fetal balling.

Ultrasonography—recommended for monitoring fetal viability; fetal stress (e.g., fetal heart rate sustained at < 180 bpm) or death; sustained tachycardia (> 260 bpm) indicates need for more frequent monitoring; placental separation, and character of fetal fluids (presence of meconium or blood in amniotic fluid); fetal heart rate is normally two to three times that of the dam in bitches.

 

TREATMENT

APPROPRIATE HEALTH CARE

Inpatient—until delivery of all fetuses and the dam is stabilized.

  • Uterine inertia—initiate medical treatment if no evidence of fetal stress.
  • Ecbolic agents contraindicated in the face of possible obstructive dystocia—may accelerate placental separation and fetal death, or cause uterine rupture.
  • Hypocalcemia—bitch: administer 10% calcium gluconate at 0.2 mL/kg slowly IV (over 5–10 minutes; monitor for arrhythmia); may be repeated q4-6h as needed; queen: 0.5–1.0 mL calcium gluconate IV slowly—use with caution in cats as risk of uterine rupture is increased due to strong uterine contractions following calcium administration.
  • Hypoglycemia—administration of balanced electrolyte solution with 5–10% dextrose at a rate of 60–80 mL/kg/day IV.
  • Oxytocin—once calcium and glucose deficits are treated, microdoses of oxytocin (0.5–4.0 IU IM, SC depending on the size of the bitch and response to treatment); may be repeated at 30-minute intervals as long as delivery progresses. Consider C-section if more than three doses of oxytocin per fetus are required or more than four fetuses remain. If the bitch is not contracting adequately on her own, allow a minimum of 30 min between delivery of a fetus and the next dose of oxytocin.
  • WhelpWise™ system monitors fetal heart rates and uterine contraction patterns; extremely useful for bitches with a history of uterine inertia or with large litters to determine the need for, and response to, medical treatment.

 

Manual Delivery

  • To deliver a fetus lodged in vaginal vault:
  • Apply lubrication liberally.
  • Digital manipulation—least amount of damage to fetus and dam. Apply traction in a postero-ventral direction.
  • Instrument delivery not recommended due to inadequate space—undesirable sequelae include fetal mutilation and laceration of the dam.
  • Never apply traction to the distal extremities of a live fetus.
  • Failure to deliver a fetus located in the vaginal canal within 30 minutes—C-section indicated.

 

SURGICAL CONSIDERATIONS

  • Indications for C-section—uterine inertia unresponsive to oxytocin or a uterine inertia with more than four fetuses remaining in utero (maximizes fetal survivability); pelvic or vaginal obstruction; inability to correct fetal malposition; fetal oversize; fetal stress; in utero fetal death.
  • Elective C-section—breeds prone to dystocia; bitches with a history of dystocia; bitches with singleton or large litter size; often performed to maximize fetal survivability.

 

General Comments

  • Provide fluid therapy with a balanced electrolyte solution before, during, and after surgery.
  • The gravid uterus can compress great vessels, compromise venous return, and place pressure on diaphragm, resulting in decreased tidal volume.
  • Pregnant bitches have lower systolic BP, PO2, PCV; and higher PCO2, respiratory rates, and incidence of acidosis.
  • Pre-oxygenation of patients improves maternal and neonatal outcome.
  • Premedication with glycopyrrolate if fetal heart rates are normal (bitches: 0.01 mg/kg IV, IM; queens: 0.005–0.01 mg/kg IV, IM); or if fetal bradycardia exists with atropine (bitches: 0.02–0.04 mg/kg IM; queens: 0.04 mg/kg IM); induction with propofol (4–6 mg/kg IV), intubate and maintain with sevoflurane (or isoflurane) preferred; propofol CRI until fetuses delivered, then switch to sevoflurane/isoflurane.
  • If propofol is unavailable, premedication with diazepam (0.1–0.4 mg/kg IV, IM) and butorphanol (0.2–0.4 mg/kg IM) followed by masking with sevoflurane (or isoflurane).
  • Ketamine—not recommended in the bitch due to fetal depression; may be used in the queen where ketamine affects the fetus in a dose-dependent manner. With appropriate premedication a low-dose induction (1 mg/kg IV or 5 mg/kg IM) may be adequate.
  • Epidural—bitch: (0.2 mg/kg 0.5% bupivacaine and 0.1 mg/kg preservative-free morphine or 0.1–0.3 mL/kg 2% lidocaine without epinephrine given to desired effect but not to exceed 10 mg/kg total lidocaine dose; queen: 2% lidocaine (0.2 ml/kg) given to desired effect plus butorphanol (0.2–0.4 mg/kg IV, IM); local anesthesia may also be utilized. Disadvantages of local/regional anesthesia are the inability to oxygenate adequately without an endotracheal tube and increased regional blood flow making hemostasis more difficult. Severely depressed or exhausted queen—premedication with diazepam (0.2–0.4 mg/kg IV, IM) or midazolam (0.066–0.22 mg/kg IV, IM) and either butorphanol (0.2–0.4 mg/kg IV, IM) or oxymorphone (0.1–0.4 mg/kg IV, IM); followed by propofol induction and maintenance with sevoflurane or isoflurane.
  • Butorphanol (0.1–0.4 mg/kg IV, IM) or buprenorphine (0.005–0.01 mg/kg IV/IM) for postoperative analgesia.
  • Premedications—if using diazepam, reverse neonates with flumazenil (0.01 mg/kg IV); if using opiates, reverse neonates with naloxone (0.04 mg/kg IV, IM, SC); repeat dosing until medications are fully metabolized in the neonate. Avoid premedication if fetal stress exists.

 

MEDICATIONS

CONTRAINDICATIONS

Oxytocin—contraindicated with obstructive dystocia, fetal stress, long-standing in utero fetal death, uterine rupture, uterine torsion.

 

FOLLOW-UP

PREVENTION/AVOIDANCE

  • Schedule elective C-section for bitches with abnormal pelvic canal; small pelvis; vaginal vault abnormalities; breeds predisposed to dystocia; dams with previous history of uterine inertia.
  • Scheduling of surgery—extremely important that D1 diestrus, LH peak, or ovulation is identified during breeding to ensure acceptable fetal survivability (see Breeding, Timing). If ovulation timing is not available, gestational aging and maturation assessment via ultrasonography is necessary.

 

EXPECTED COURSE AND PROGNOSIS

  • If dystocia is identified promptly and intervention is successful—good to fair for life of the dam; fair for survival of fetuses.
  • If dystocia unrecognized or untreated for 24–48 h—poor to guarded for life of the dam; unlikely that any fetuses will survive.

 

MISCELLANEOUS

PREGNANCY/FERTILITY/BREEDING

History of dystocia may or may not impact future fertility. Dystocia may recur depending on cause (anatomic abnormalities, primary uterine inertia). Resolution of dystocia by C-section does not preclude natural whelping during future deliveries.

 

ABBREVIATIONS

C-section = cesarean section

LH = luteinizing hormone

PCO2 = partial pressure of carbon dioxide

PCV = packed cell volume

PO2 = partial pressure of oxygen