Background & Aim: An increased duration of the second stage of labor is a time of particular anexiety for midwives. It is believed that the longer second stage of labor takes the higher risk for fetus and mother. The ideal length of second stage of labor is poorly defined. Moreover an increased duration of second stage of labor is often a time when mothers and midwives are physically and mentally exhausted. The aim of this study was to investigate the impact of maternal parameters influencing the duration of the second stage of labor in vaginal deliveries.
 Material and Methods: This study was a descriptive – cross sectional research which has been conducted between 2006- 2007. There were 804 consecutive patients delivering of a singleton fetus in cephalic presentation in 3 governmental hospitals in Tehran. A population of 400 nulliparous women and 404 multiparous women with spontaneous vaginal deliveries were analyzed. Descriptive statistics are reported for maternal age, maternal weight gain during pregnancy, parity, the duration of induction, the cervical dilatation on admission and the dilation of cervix at which water bag intentionally was ruptured.
 Results: The mean duration of second stage of labor was 52.4 min in nuliparous and 20.89 min in multiparous. Univariate analysis identified, maternal weight gain (P=0.019), and t test identified parity (p < 0.001), maternal age, cervical dilatation on admission (p < 0.001), cervical dilatation at which membrane was ruptured (P=0.006) as significantly correlated with second stage duration.
 Conclusion: Our data show a correlation between the policy of active management of labor and an increased second stage of labor. We conclude that a less intervention attitude towards labor can improve the progress of it. We suggest that every labor progress should be evaluated individually taking into account the maternal factors.