When Labour Stalls: Recognising and Managing Primary Uterine Inertia in Dogs

Dystocia is one of the most critical reproductive emergencies encountered in small animal practice. Delayed recognition or inappropriate management can rapidly compromise both maternal and fetal survival. Studies estimate that dystocia occurs in approximately 5–16% of canine pregnancies, making it a relatively common challenge for veterinary practitioners¹. 

Among the various causes of dystocia, Primary Uterine Inertia (PUI) is the most frequently encountered, accounting for nearly 75% of dystocia cases in bitches^1,2. 

Understanding Primary Uterine Inertia 

Primary uterine inertia refers to the inability of the uterus to generate contractions that are strong or sustained enough to expel fetuses during parturition. As a result, labour either fails to progress or stops prematurely despite the presence of viable puppies³. 

Clinically, PUI is classified into two forms: 

• Complete Primary Uterine Inertia – The bitch fails to initiate the second stage of labour, and no puppies are delivered.

• Partial Primary Uterine Inertia – Labour begins normally, but uterine contractions cease before all fetuses are expelled.

Why Does Primary Uterine Inertia Occur? 

The condition is multifactorial, with several maternal and metabolic factors contributing to inadequate uterine contractions. 

Common predisposing factors include¹: 

• Hypocalcaemia

• Obesity

• Uterine infections or septicemia

• Lack of exercise

• Debility and advanced age

• Pain-associated voluntary inhibition of labour

• Behavioural or psychological disturbances during parturition

PUI is also reported more frequently in bitches carrying very small litters, where insufficient fetal stimulation may fail to trigger effective labour. Conversely, excessive fetal numbers in small breeds can also contribute to uterine exhaustion and poor contractility. 

Clinical Recognition: Two Illustrative Cases 

A recent report described two bitches presenting with signs suggestive of dystocia caused by primary uterine inertia¹. 

The first case involved a two-year-old Pomeranian presented 65 days after mating. Despite signs of restlessness and an open cervix, no puppy had been delivered. Vaginal examination revealed a relaxed birth canal, while ultrasonography confirmed the presence of a live full-term fetus. The findings were consistent with complete primary uterine inertia. 

The second case involved a one-year-old American Pit Bull presented 60 days after mating with nesting behaviour, panting, anorexia, vomiting, and green vaginal discharge. Ultrasonography confirmed multiple live fetuses with normal fetal heart rates exceeding 200 beats per minute. Based on clinical findings and imaging, the bitch was diagnosed with PUI. 

Medical Management: When Intervention Can Restore Labour 

Successful management of primary uterine inertia depends on accurate diagnosis and confirmation that there is no fetal obstruction. 

In both cases, treatment included: 

• Intravenous dextrose supplementation

• Calcium gluconate administration

• Low-dose oxytocin therapy

Calcium plays a crucial role in uterine muscle contraction, while oxytocin stimulates myometrial activity. Together, these therapies can restore effective labour when uterine responsiveness is preserved. 

In the Pomeranian, uterine contractions resumed after treatment. One live puppy was delivered with the assistance of whelping forceps, followed shortly by another live puppy delivered naturally. A third stillborn fetus was subsequently expelled after repeat oxytocin administration. 

The bitch recovered uneventfully and returned to normal health within a week¹. 

When Medical Therapy Fails 

Not all cases respond to medical management. 

In the Pit Bull, despite calcium supplementation and repeated oxytocin administration, uterine contractions remained inadequate for fetal delivery. A cesarean section was therefore performed, resulting in the successful delivery of three live puppies. 

Researchers suggested that failure to respond may be associated with reduced sensitivity or downregulation of oxytocin receptors in the uterine muscle¹. Prolonged exposure to endogenous oxytocin during dystocia can also desensitize receptors, reducing the effectiveness of medical treatment⁴. 

In such cases, delaying surgical intervention may unnecessarily increase fetal and maternal risk. 

Practical Takeaways for Clinicians 

Primary uterine inertia remains one of the leading causes of canine dystocia and requires prompt evaluation. Ultrasonography plays a critical role in assessing fetal viability and guiding treatment decisions. 

Medical management using calcium and oxytocin can be highly effective in appropriately selected cases. However, clinicians should closely monitor response and be prepared to proceed to cesarean section when uterine contractions fail to resume or fetal compromise is suspected. 

Early intervention, accurate diagnosis, and timely decision-making remain the key factors that determine successful outcomes for both the bitch and her puppies. 

References

1. Jyothi K, Gunaranjan KS. Management of primary uterine inertia in female dogs. Ind. J. Canine. 2023:118-20. http://www.indianjournalofcaninepractice.com/december2023/IJCP-December-2023-Vol-15-iss-2-pp118-120.pdf

2. Balogh O. When physiology fails: Endocrine and clinical perspectives on complicated pregnancy and parturition outcomes in dogs. Journal of Reproduction and Development. 2026;72(3):390-7. https://www.jstage.jst.go.jp/article/jrd/72/3/72_2025-133/_pdf 

3. Steiner M, Schuler G, Frehner BL, Reichler IM, Goericke-Pesch S, Balogh O, Tavares Pereira M, Kowalewski MP. Primary uterine inertia (PUI) in dogs is associated with impaired placental availability of factors involved in the parturition cascade. Animals. 2025 Oct 20;15(20):3043. https://www.mdpi.com/2076-2615/15/20/3043

4. Tamminen T, Sahlin L, Masironi-Malm B, Dahlbom M, Katila T, Taponen J, Laitinen-Vapaavuori O. Expression of uterine oxytocin receptors and blood progesterone, 13, 14-dihydro-15-Keto-Prostaglandin F2α, and ionized calcium levels in dystocic bitches. Theriogenology. 2019 Sep 1;135:38-45. https://doi.org/10.1016/j.theriogenology.2019.06.007