Uterine rupture

Uterine rupture has previously been defined and referred to as uterine tear (Dolente et al., 2005; Javsicas et al., 2010; Perkins et al., 1992). More recent reporting has followed human literature using the term rupture (Agass & Gormley, 2026; Diekstall et al., 2020; Mogg et al., 2006; Offer et al., 2022; Risvanli et al., 2026; Spoormakers et al., 2016). This term describes a full thickness laceration or tear of the uterus regardless of when it occurs. The timing of rupture is important and provides for an interesting discussion as it affects presentation, management and the morbidity and mortality of both mare and foal. Uterine rupture is a well described complication of Stage 2 parturition but can also occur spontaneously or following dystocia (Javsicas et al., 2010). Uterine rupture was diagnosed in 5.5% of mares admitted to a referral hospital for post-partum colic signs and is the third most common cause of death post-partum (Dolente et al., 2005). Typical presentation is in the first 1–3 days post-partum (Dolente et al., 2005; Javsicas et al., 2010; Offer et al., 2022). Mares at risk of post-partum metritis due to placentitis during gestation are at greater risk of severe septic peritonitis following uterine rupture and account for more rapid presentation and more severe clinical signs. Rarely mares with small uterine ruptures will not be diagnosed in the immediate post-partum period. One report details a mare with infertility that resolved after repair of a chronic, partially healed uterine rupture (McNally et al., 2012). Pre-partum uterine rupture occurs rarely, presumably from chronic uterine wall stretching, ischaemia and pressure. Uterine torsion and hydrops conditions are most cited causes of pre-partum rupture, but there are rare case reports of spontaneous rupture or following toxicity (Agass & Gormley, 2026; Oruc et al., 2010; Lemonnier et al., 2022; Lofstedt, 2011; Spoormakers et al., 2016; Vasey & Russell, 2011). Uterine torsion typically occurs in the last trimester of pregnancy with acute severe colic signs. Uterine rupture was not a complication in a large group of mares where the torsion was recognised and corrected quickly (Spoormakers et al., 2016). Rarely, mares will present with partial torsion and intermittent colic over a period of days to weeks. Affected mares are at increased risk of rupture occurring spontaneously or during correction of torsion (Lofstedt, 2011; Vasey & Russell, 2011). Hydrops conditions resulted in uterine rupture in 1/30 affected mares (Lemonnier et al., 2022). The case study of the Amorphous globosus highlights challenges in diagnosis of pre-partum uterine rupture (Risvanli et al., 2026). The uterine rupture diagnosed in this mare at 375 days gestation was well tolerated despite the obvious chronicity of the condition and the dead fetus. The mean gestation period for mares is 340 days with a range of 330–360 days (Christianson, 2011). The difficulty in predicting when a mare will foal delayed diagnosis in this mare. Evaluation to ensure the fetus is alive and that the overdue mare is still pregnant is recommended and prompted diagnosis in this case. The mare was running milk from her udders which can be a complication of placentitis and would further support the owner's decision for evaluation of this overdue mare. Clinical signs will depend upon the severity of the peritonitis and are not specific but include depression, colic, tachycardia and fever. Rarely, intestinal herniation occurs through the rupture. Mares may present with subtle signs in the early stage of disease, which complicates diagnosis (Javsicas et al., 2010; Offer et al., 2022). Continued monitoring for development of fever or other clinical signs is important in the days following parturition. Uterine palpation is limited by the large size of the uterus post-partum. Retained foetal membranes may delay or complicate a diagnosis. Rupture of the uterine horns was palpated pre-operatively in 24% of cases. Uterine body rupture occurred in 26% of cases but 100% could be palpated (Javsicas et al., 2010). Despite this, uterine palpation is vital for surgical planning as a tear near the cervix will be difficult to access and impossible to repair in a mare via a ventral midline incision. Rectal evaluation should be performed carefully in mares with colic in the post-partum period. Broad ligament haemorrhage typically is seen immediately post-partum and is not associated with fever but can occur concurrently with other conditions. It is an important differential due to the risk of the clot dislodging, causing fatal haemorrhage. Rectal evaluation in heavily sedated mares provides important information for diagnosis and treatment. Clinical signs depend upon the underlying cause, from more subtle chronic signs to colic and SIRS. The lack of observed clinical signs in this case report has been previously described (Lofstedt, 2011). Rectal palpation depends on the position and length of the rupture. Case studies report feeling a foal's foot outside the uterus or, as in this case report, being able to directly palpate the fetus without the spongy feeling of the uteroplacental wall (Perkins et al., 1992; Risvanli et al., 2026). One report recorded the fetus had fallen through the ruptured uterus into the abdomen and could not be reached by rectal palpation (Lofstedt, 2011). Uterine torsion presents with mild, intermittent pain to severe colic signs. Subtle clinical signs can delay presentation (Spoormakers et al., 2016). Equine uterine torsion occurs cranial to the cervix and is diagnosed by rectal palpation. Hydrops amnion or allantois is initially well tolerated, which delays presentation. Abdominal distension, discomfort, premature udder development, anorexia, vaginal discharge and ventral oedema are reported (Lemonnier et al., 2022). Rectal palpation is suggestive of a large domed uterus above the pelvic brim and difficulty in balloting the fetus. Haematology reflects the resulting peritonitis. WBCC is typically normal to low with toxic neutrophils and normal to elevated fibrinogen (Dolente et al., 2005; Javsicas et al., 2010; Offer et al., 2022). Elevated PCV and lactate reflect hypovolaemia though are often in the normal range (Dolente et al., 2005; Javsicas et al., 2010; Offer et al., 2022). A late term mare with spontaneous pre-partum uterine rupture in our hospital presented with blood work suggestive of uroperitoneum due to the absorption of allantoic and amnionic fluid from the peritoneum. The mare had significant azotaemia, increased potassium and phosphorus. The classic finding is an increase in peritoneal fluid. Echogenicity, volume and presence of fibrin will depend upon the severity of peritonitis. Depending upon the site of rupture, the uterus may contain fluid. A large volume of swirling, smoky fluid is diagnostic of haemorrhage but does not exclude a diagnosis of uterine rupture. Rarely, severe cases of chronic peritonitis may result in thickening of the intestinal walls and signs of ileus. Increased peritoneal fluid in the pre-partum mare is abnormal. Descriptions of uterine rupture are described to imply the ultrasound examination is straightforward, but careful evaluation is needed to determine the presence or absence of the uteroplacental wall separating the fetus from the mare's abdominal organs (Agass & Gormley, 2026; Vasey & Russell, 2011) (Figures 1 and 2). Diagnosis of hydrops is via rectal and transabdominal ultrasound findings of allantoic fluid with a maximum depth greater than 18 cm. Repeat examinations to confirm consistent increase in allantoic fluid is recommended due to a wide range of normal (4.7 to 22 cm, mean of 13.4 ± 4.4 cm) (Slovis & Irvin, 2023). Abdominocentesis with cytology and culture of the sample is essential for presumptive diagnosis of a uterine rupture. Sampling can be aided by ultrasound guidance. Hypovolaemic shock may limit the volume of peritoneal fluid and correction by intravenous fluid therapy can increase the likelihood of obtaining a sample. Fluid returned is serosanguinous to frank haemorrhage (Dolente et al., 2005; Javsicas et al., 2010; Offer et al., 2022). Peritoneal WBCC is important for diagnosis of peritonitis. Parturition does not raise WBCC above 5 × 109, though it may increase to 13 × 109 at 2 days post-partum (Frazer et al., 1996). WBCC is typically higher in post-partum mares with urogenital tract disruption than gastrointestinal disease, and this is presumed to be due to the more chronic development of peritonitis in these mares (Offer et al., 2022). Diagnosis of uterine rupture is suggested by neutrophilia, toxic neutrophils and bacteria. A low WBCC does not exclude the presence of rupture in the early stage of disease. Plant material and protozoa is seen with enterocentesis or intestinal rupture. Plant material was present on abdominocentesis from a large uterine body tear in one mare (Offer et al., 2022). Haemorrhagic fluid must be evaluated for elevated WBCC suggesting its source is a lacerated blood vessel of the torn uterine wall (Mogg et al., 2006; Offer et al., 2022). If a mare with haemoabdomen becomes febrile or develops evidence of inflammation on peripheral blood work, repeat abdominocentesis for evidence of septic peritonitis is recommended. Peritonitis from a ruptured bladder is differentiated from uterine rupture by elevated peritoneal creatinine and endoscopy of the bladder. Abdominocentesis is more challenging due to the gravid uterus but can be aided by ultrasound guidance. Sampling may not be possible in chronic cases with small volumes of peritoneal fluid (Vasey & Russell, 2011). The mare in our hospital had an elevated peritoneal creatinine and a normal bladder on endoscopy. Treatment must begin medically by correcting hypovolaemic shock and treating the signs of SIRS. Placement of an abdominal drain allows removal of peritoneal fluid and lavage of the abdomen. Abdominal drains can be problematic over time, with poor outflow secondary to blockage by omentum or fibrin. Outcome, period of hospital stay or hospital cost was similar in 11 medically treated mares compared with 26 surgically treated mares (Javsicas et al., 2010). Successful repair by laparoscopy has been reported (Diekstall et al., 2020; McNally et al., 2012). Exploratory laparotomy is preferentially performed in our hospital as it has the advantage of accurate diagnosis and repair of the uterine rupture, allows evaluation for other complications and ligation and removal of omentum improves post-operative abdominal drainage and lavage. Antimicrobial therapy is initially broad spectrum but directed by abdominocentesis culture results. Ice boots to reduce the risk of laminitis are recommended. Severe peritonitis may result in ileus requiring regular removal of gastric reflux. Prognosis for discharge has been reported as 63%–80% (Dolente et al., 2005; Javsicas et al., 2010; Offer et al., 2022). Reports of fertility in survivors of 13/26 in foal in that breeding season and 23/26 producing at least one foal in subsequent breeding seasons (Javsicas et al., 2010). The underlying cause of the pre-partum uterine rupture must be addressed as soon as possible. Uterine torsion resulting in pre-partum rupture is a surgical emergency. A live foal was delivered from a mare where the torsion was corrected by flank approach and the foal delivered through the cervix (Perkins et al., 1992). The uterus was then sutured, and the mare was able to have future foals. Ventral midline approach for delivery of a live foal from the abdomen has been reported (Agass & Gormley, 2026). None. No conflicts of interest have been declared. Not required for this clinical commentary.