What is the role of tone in the etiology of postpartum hemorrhage (PPH)?

Updated: Jun 27, 2018
  • Author: John R Smith, MD, FACOG, FRCSC; Chief Editor: Ronald M Ramus, MD  more...
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Answer

Uterine atony and failure of contraction and retraction of myometrial muscle fibers can lead to rapid and severe hemorrhage and hypovolemic shock. Overdistension of the uterus, either absolute or relative, is a major risk factor for atony. Overdistension of the uterus can be caused by multifetal gestation, fetal macrosomia, polyhydramnios, or fetal abnormality (eg, severe hydrocephalus); a uterine structural abnormality; or a failure to deliver the placenta or distension with blood before or after placental delivery.

Poor myometrial contraction can result from fatigue due to prolonged labor or rapid forceful labor, especially if stimulated. It can also result from the inhibition of contractions by drugs such as halogenated anesthetic agents, nitrates, nonsteroidal anti-inflammatory drugs, magnesium sulfate, beta-sympathomimetics, and nifedipine. Other causes include placental implantation site in the lower uterine segment, bacterial toxins (eg, chorioamnionitis, endomyometritis, septicemia), hypoxia due to hypoperfusion or Couvelaire uterus in abruptio placentae, and hypothermia due to massive resuscitation or prolonged uterine exteriorization. Recent data suggest that grand multiparity is not an independent risk factor for PPH.


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