Uterine activity during the two hours after placental delivery among low-risk pregnancies: an observational study

The purpose of this study was to describe uterine activity within the first two hours after placental delivery among low-risk pregnant women.

Participants were 17 low-risk pregnant women who had a singleton birth at midwifery birth centers in Japan. Contractile waves of uterine activity were measured by using an external tocodynamometer.

Spontaneous uterine contraction frequency during the first two hours after the placental delivery decreased over time (F_9, 54=19.7, p < 0.001). The mean contraction intervals were 1.9 ± 0.3 min, 2.4 ± 0.9 min, 4.2 ± 0.7 min and 7.9 ± 2.1 min for the second stage, third stage, and the first hour and second hour after placental delivery, respectively. Uterine contraction frequency increased with oxytocin administration and infant suckling; however, an icepack to cool the uterus did not change the contraction waves. No correlations were found between uterine activity and blood loss or pain.

Contraction of the myometrium is the primary mechanism for hemostasis. The uterine contraction intervals became prolonged over time, and blood loss did not increase. The findings provide insight into the role of myometrium contraction as a hemostasis mechanism.