Study design: Randomized control trial study.

Setting: Labor unit, Department of Obstetrics and Gynecology, Phramongkutklao Hospital.

Subjects: 120 term singletons, nulliparous with cephalic presentation pregnant women who had spontaneous labor and came to labor room from June 1st, 2013 to October 31th, 2013.

Material and Method: After signed the consent form, the selected pregnant women were divided into two groups by random number table. The early amniotomy which performed when patients entered the active phase of labor (cervical dilatation 3-5 cm., n=60), and the late amniotomy which membrane was left intact and amniotomy was reserved for specific indications (n=60). The outcome of labor was recorded by the attending physicians. Main outcome measures: Compare the duration of labor between two groups.

Results: The time of first stage of labor was not different between early and late amniotomy groups (560.0 vs. 637.5 min; p<1.0; time difference 77.5 minutes). There was statistically significant difference between women in the early amniotomy and control groups in cesarean section rate (43.3% vs. 20%; p = 0.006).

Conclusion: The amniotomy should not be introduced routinely as the standard labor management, because it was not proven to shorten the course of labor. The authors recommend that the women be informed about the results of the amniotomy, then the decisions were made between the women and their caregivers.

Keywords: Duration of labor, Amniotomy, Cesarean section rate