Dystocia

• Definition: difficulty delivering fetus(s) from the uterus through the birth canal (vagina, vestibule, vulva) normally resulting in birth.
• Outcome: fetal and/or maternal morbidity and mortality, fading neonates, post-artum metritis.
• Cause: fetal, maternal, combination.
• Fetal:
  • Fetal abnormalities (hydrops fetalis, anasarca, hydrocephalic, twins).
  • Abnormal fetal position (fetal dorsum normally closest to dam dorsum; fetal ventrum closes to dam dorsum problematic) or posture (diving stance is normal, head elevation and shoulder flexion problematic).
  • Fetus exiting one horn and entering the other, blocking entrance into the uterine body.
  • 50% of canine fetuses are caudad (breech in humans) presentation, 50% cephalad, considered normal variation. Caudad can be problematic if pelvic limbs are in flexion.
• Maternal:
  • Uterine inertia (primary Primary uterine inertia, secondary), herniation, adhesins, torsion, hydrops, lack of allantoic fluid, rupture.
  • Birth canal abnormalities: steep pelvic floor (brachycephalics), vaginal septum, stricture, vulvar edema.
• Combination:
  • Mismatch between fetal size and birth canal dimensions (brachycephalics, chondrodystrophics, small litter size in breeds with litters typically >6 fetuses).
  • Singleton pregnancy: eventual fetal oversize +/- failure to initiate whelping (lack of fetal stress) causing prolonged gestation.
• Treatment: depends on cause/type of dystocia. Supportive and specific (see below).
• Prognosis: guarded to good.

• English Bulldog Bulldog.
• Boston Terrier Boston Terrier.
• Pug Pug.
• French Bulldog French Bulldog.
• Chihuahua Chihuahua.

• Varies based on medical vs surgical management, +/- emergency complications.

• Maternal vs Fetal (see above); combination of maternal and fetal causes most common.

Deviation from normal labor

Stages of normal labor

• First: uterine contractions increasing in frequency and duration. Normally 12-24 h in duration. Preceded by temperature drop to less than 99°F (37.2°C) accompanying luteolysis and progesterone decline to <2 ng/mL, occurring 12-24 h earlier.

• Second: uterine contractions + abdominal efforts → neonatal delivery.

• Third: placental delivery (normally with fetus, can occur up to 24 h after).
  • Bitches normally transition from stage 2 to stage 3 until entire delivery is complete.

Clues to diagnosis/clinical signs

• Failure to initiate labor at term:
  • Must confirm gestation length determination.
• Failure to proceed from stage 1 to stage 2, within 24 h.
• Failure to deliver all in timely manner (less than 8 h; 4-5 h ideal).
• Fetal or maternal distress:
  • Fetal: cyanotic, difficult to resuscitate, stillborn.
  • Maternal: hypotension, anemia, exhaustion, shock.
• Greater than 1 h stage 2 without delivery of neonate.
• Copious vaginal hemorrhage.
• Uteroverdin (green vulvar discharge indicating placental separation) without immediate delivery.
• Irreversible and unrecognized history of dystocia (vaginal strictures, uterine adhesions).

Tools to diagnose

• History (ovulation timing Ovulation detection), physical examination including vaginal examination Vaginal examination (digital or vaginoscopic Cystoscopy: transurethral cystoscopy -vaginoscopy):
  • Term pregnancy is 56-58 days from diestrus day 1 or 66-64 days from the initial rise in progesterone Progesterone assay or the LH surge.
• Stat CBC Hematology: complete blood count (CBC), chemistries (BUN Blood biochemistry: urea, BG Blood biochemistry: glucose), electrolytes (iCa+ Blood biochemistry: ionized calcium), urine dipstick Urinalysis: dipstick analysis (ketones? Urinalysis: ketone).
• Radiography Radiography: abdomen (actually pregnant?, size and number of fetuses present? Fetal maturation (dentition visible?)        .
  • Can indicate immediate surgical intervention rather than medical treatment (singleton).
  • Can identify completion of labor when owner misinterprets litter size.
• Ultrasound Ultrasonography: uterus (viable, stressed?)  .
  • Fetal HR should be >180-200 bpm.
  • Degree of bradycardia reflects degree of fetal stress.
  • Serial ultrasound permits evaluation of fetal response to medical therapy (bradycardia resulting from administration of calcium or oxytocin is a contraindication to further medial therapy).
  • Can identify fetal abnormalities (anasarca).
  • Can identify retained placentae.
• Fetal doppler:
  • Permits evaluation of fetal heartrates, more technically challenging to find every fetus compared to ultrasound.
• Tocodynamometry (gold standard):
  • Permits actual evaluation of myometrial activity:
    • Frequency of contractions:
      • Normal 1-12 contractions/hr.
    • Strength of contractions:
      • Normal 15-40+ mm Hg.
    • Duration of contractions:
      • 2-5 minutes.
  • Idenitifies abnormal activity (uterine torsion, rupture) indicating need for immediate Caesarean section.

• Initiate fluid support (5% dextrose in lactated Ringers).
• Correct any clinical pathology abnormalities identified (hypoglycemia, hypocalcmia, severe anemia).

Specific therapy

• Physical manipulation of obstructive dystocia difficult in the canine due to fetal fragility and small birth canals:
  • Manipulation to reposition a fetus in the distal vaginal canal can be possible:
    • Liberal use of lubrication (can pass through red rubber catheter at or cranial to the fetus).
    • Avoid forceful traction or instrumentation.
    • Gentle traction along path of vulva (towards the bitch's hocks) possible.
    • Elevating the bitch's forequarters can help.
• Medical therapy as supported by clinical evaluation above:
  • Calcium gluconate Calcium gluconate (administer first):
    • Improves strength of myometrial contractions (delivery can occur with monotherapy).
    • Serum iCa Blood biochemistry: ionized calcium levels are usually normal:
      • 10% calcium gluconate 1 ml (0.465 mEq Ca+)/4.4 kg SC q 4-6h.
    • Detectable response to administration of calcium despite eucalcemia:
      • Intracellular mechanism of action.
  • Oxytocin Oxytocin:
    • Increases frequency of myometrial contractions.
    • Oxytocin (administer second if needed):
      • 10 U/mL 0.25-2.0 units per dam SC or IM q30-60 min.
    • Excessive doses of oxytocin cause tetanic myometrial contractions and can promote uterine rupture and worsen fetal hypoxia.

Surgical therapy: Caesarean section

• When medical therapy fails or is contraindicated:
  • Fetal distress (worsening fetal bradycardia).
  • Refractory inertia.
  • When tocodynamometry shows an aberrant pattern or obstructive pattern.
  • When maternal compromise is evident, after stabilization.

Refereed papers

• Recent references from PubMed and VetMedResource.
• O'Neill D G, O'Sullivan A M, Manson E A et al (2019) Canine dystocia in 50 UK first-opinion emergency care veterinary practices: clinical management and outcomes. Vet Rec 184, 409 PubMed.
• Gendler A, Brourman J, Graf K, Richards J, Mears E (2007) Canine dystocia: medical and surgical management. Compend Contin 29 (9), 551-62 VetMedResource.
• Bergstrom A, Nodtvedt A N, Lagerstedt A S, Egenvall A (2006) Incidence and breed predilection for dystocia and risk factors for cesarean section in a Swedish population of insured dogs. Vet Surg 35 (8), 786-791 PubMed.
• Davidson A P (2001) Uterine and fetal monitoring in the bitch. Vet Clin Small Anim Pract 31 (2), 305-313 PubMed.
• Eneroth A, Linde-Forsberg C, Uhlhorn M & Hall M (1999) Radiographic pelvimetry for assessment of dystocia in bitches - a clinical study in two terrier breeds. JSAP 40 (6), 257-264 PubMed.
• Darvelid A W & Lindeforsberg C (1994) Dystocia in the bitch - a retrospective study of 182 cases. JSAP 35 (8), 402-407 VetMedResource.