Staircase sign: a newly described uterine contraction pattern seen in rupture of unscarred gravid uterus.

Although extremely rare, rupture of an unscarred gravid uterus poses significant morbidity and mortality to both fetus and mother. In the past, loss of uterine contraction was thought to be characteristic of uterine rupture, while recent evidence shows that uterine contraction pattern is not associated with uterine rupture. We report two cases of rupture in the unscarred term uterus. Both patients were multiparous and denied any past medical complications, previous cesarean delivery or myomectomy. Uterine rupture occurred in the latent phase of labor at 1 cm dilation (Case 1) and during an intravenous oxytocin infusion after three doses of intravaginal misoprostol (Case 2). Case 2 required cesarean hysterectomy and blood transfusion. Case 1 was monitored with an external tocodynamometer, while Case 2 was monitored with an internal pressure transducer. External monitoring demonstrated the classic sign of complete loss of uterine tone. In contrast, internal monitoring demonstrated an increase in uterine resting tone. Both techniques revealed a stepwise gradual decrease in contraction amplitude followed by sudden onset of profound and prolonged fetal bradycardia (staircase sign). In cases of uterine rupture, differing baseline characteristics between contraction patterns were dependent on uterine monitoring technique. In both techniques a stepwise gradual decrease in contraction amplitude was followed by prolonged fetal bradycardia.