Classification

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  Complete uterine rupture involves the full thickness of the uterine wall, with or without expulsion of the fetus and/or placenta and includes rupture of the membranes at the site of rupture. It usually presents as a dramatic emergency which threatens the life of both the woman and her baby, particularly if there is any delay in performing laparotomy.

  
  
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  Incomplete rupture or uterine dehiscence occurs when the uterine wall ruptures but the visceral peritoneum remains intact. It is usually asymptomatic and the diagnosis is made incidentally at the time of caesarean section. The time interval between incomplete rupture and diagnosis is usually unknown and incomplete rupture is rarely associated with adverse clinical outcomes. It often goes unrecorded and therefore case ascertainment is unreliable. It is recommended that the term ‘dehiscence’ be reserved for incomplete rupture and that such cases be excluded from clinical studies of uterine rupture because the impact is clinically of little consequence.

Causes

Complete uterine rupture may occur with either a previously scarred or an unscarred uterus. In high-income healthcare settings complete rupture occurs most commonly in the presence of a previously scarred uterus, but in low income healthcare settings complete rupture often occurs in an unscarred uterus following unsupervised obstructed labour.

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  Despite the frequent use of oxytocics to induce or augment labour, rupture of the uterus in a primigravida is extraordinarily rare, particularly in the absence of a congenital uterine malformation or trauma. Rupture in the absence of trauma in a primigravida raises questions about previously undisclosed uterine surgery or perforation.

  
  
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  Traumatic uterine rupture is uncommon. Antepartum, the trauma is usually the result of an accident or violence. In such circumstances, the threat to life is high because there may be other injuries and the pregnant woman may not be under medical supervision. Peripartum traumatic rupture may occur when a prolonged labour is inadequately supervised or when an obstetric manoeuvre or operative vaginal delivery goes badly wrong. This is more likely to occur and is more likely to end in catastrophe in poorly resourced countries.

  
  
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  Rupture of a scarred uterus is usually associated with a history of previous caesarean section. The type of the previous caesarean matters. The risk of rupture after a low transverse caesarean ranges from 0.2 to 1.5%. More recent American reviews quote a rate of 0.5−1.0%, which is higher than the 0.2% cited in European studies. The risk of uterine rupture quoted for a trial of labour after a caesarean delivery varies widely in national guidelines; although the experts presumably reviewed a similar body of scientific evidence.

  
  
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  A 4−9% rupture rate after a previous classical or T-incision caesarean is quoted. There is uncertainty about the risk of rupture if the previous vertical incision was confined to the lower uterine segment.

  
  
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  Rarely, uterine rupture may complicate delivery following a previous myomectomy, or a uterine perforation which may or may not have been diagnosed at the time. It may also complicate previous uterine surgery such as a metroplasty or cornual resection of an ectopic pregnancy. It has been suggested in the past that the risk of rupture is only increased if the previous surgery involved the full thickness of the uterine wall but evidence to support this is lacking.

Prevention and early diagnosis of uterine rupture in clinical practice are more likely to be successful when a detailed obstetric and gynaecological history is taken at the first antenatal visit. Uterine rupture after previous scarring confined to a low transverse uterine incision may present intrapartum or postpartum and thus the commonest presentation of uterine rupture in developed countries occurs under midwifery or obstetric supervision. Uterine rupture after previous scarring involving the uterine body may present antepartum, intrapartum or postpartum. Indeed, antepartum rupture of a vertical scar may occur remote from term and outside hospital. Thus, rupture with a vertical scar on the uterine body may be associated with higher risks of an adverse clinical outcome.

Clinical Presentation

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  Uterine rupture complicating a previous low transverse caesarean section commonly presents intrapartum with fetal heart rate abnormalities. Thus, it is recommended that women with previous uterine surgery should have continuous electronic fetal heart rate monitoring in labour. If there are heart rate abnormalities, the diagnosis of rupture should be immediately considered and delivery expedited. The time taken to perform a fetal scalp blood pH for evidence of fetal hypoxia may incur a delay which can be catastrophic if the fetal heart abnormalities are due to uterine rupture. Therefore, early recourse to an emergency caesarean is advisable if there is evidence of fetal compromise in women labouring with a previous uterine scar.

  
  
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  Intrapartum uterine rupture may also present with cessation of uterine contractions and, therefore, any decision to augment labour with oxytocin should only be made with great caution after clinical assessment by an experienced obstetrician.

  
  
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  There may be a history of constant rather than intermittent abdominal pain. Tenderness over a previous caesarean scar is a non-specific symptom and not particularly helpful in making the diagnosis.

  
  
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  Uterine rupture may be associated with haemorrhage which can precipitate clinical shock. Abdominal tenderness or shock which appears disproportionate to any blood loss should raise the suspicion of concealed intra-abdominal bleeding. Primary postpartum haemorrhage unresponsive to the normal treatment, including oxytocics, in a woman with a scarred uterus should also raise the suspicion of rupture.

  
  
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  If the rupture involves the bladder, haematuria may persist before or after delivery.

  
  
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  Alteration in the shape of the uterine swelling on abdominal examination is described; however, this may not occur until part of the uterine contents have been expelled into the abdominal cavity.

  
  
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  Antepartum uterine rupture is rare but should be considered in any woman with a uterine scar who presents with abdominal pain or tenderness, particularly in association with clinical shock and a fall in haemoglobin concentration. If a previous caesarean section has been performed preterm the possibility of a vertical uterine incision should be considered. Ideally, the notes from all previous caesareans should be available and scrutinized by an obstetrician at the first antenatal visit.

  
  
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  Blunt trauma, unless substantial, is a rare cause of uterine rupture and usually presents before delivery with a history of an accident or violence.

  
  
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  Uterine rupture associated with obstetric trauma is manifest at the time or shortly after an obstetric manoeuvre or operative delivery when the obstetrician is still present.