Postpartum Hemorrhage: Uterine Atony
A 37-year-old woman, gravida 4 para 3, delivers vaginally at 40 weeks. During placental delivery the uterus inverts, and she bleeds 1200 mL. Blood pressure is 84/50 mm Hg and pulse 128 beats/min. The genital tract shows no lacerations and coagulation studies are normal. Which of the following best explains her postpartum hemorrhage?
- A.Trauma to the pelvic blood vessels
- B.Vaginal and cervical laceration
- C.Inadequate myometrial contractionCorrect
- D.Local endometrial coagulopathy
Explanation
Haemostasis after delivery depends almost entirely on mechanical compression of the spiral arteries by contracting interlacing myometrial fibres, the so-called living ligatures, rather than on the clotting cascade. In uterine inversion the fundus is turned inside out and the myometrium cannot contract effectively around the placental bed, so the open sinuses continue to bleed and the loss is rapid and large. This is why inversion falls under the tone category of the four Ts of postpartum haemorrhage, alongside trauma, tissue and thrombin. The clinical detail in this case excludes the alternatives explicitly: the genital tract is intact, so trauma and laceration are not responsible, and the coagulation studies are normal, excluding thrombin causes such as disseminated intravascular coagulation. Shock in inversion is often disproportionate to the measured loss because traction on the infundibulopelvic ligaments produces a strong vagal response with bradycardia and hypotension. Management is immediate manual replacement of the fundus before a cervical constriction ring develops, withholding uterotonics until the uterus is back in position, then giving oxytocin and other uterotonics to restore tone, with parallel resuscitation, cross-matched blood and tranexamic acid. Failure of manual replacement leads to hydrostatic replacement or surgical correction.
Why each option
- A.
- Vascular trauma would require an identifiable injury such as a broad ligament or paravaginal haematoma, and the genital tract here is intact.
- B.
- Lacerations were specifically excluded on examination, so trauma is not the mechanism of this bleed.
- C.
- Correct. The inverted uterus cannot contract around the placental bed, so failure of myometrial contraction leaves the sinuses open and bleeding.
- D.
- Coagulation studies are normal, excluding a thrombin cause. Coagulopathy may develop later as a consequence of massive loss rather than as the initial cause.
Reference: ACOG Practice Bulletin No. 183, Postpartum Hemorrhage, reaffirmed 2024
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