Objective: To compare labor pattern at 4cm and 6 cm cervical dilatation in spontaneous labor in low risk nulliparous women. Design: A prospective observational study. Setting: The study was conducted in a tertiary referral center of India. Population: Study involved 500 low risk nulliparas; singleton term pregnancy; vertex presentation in spontaneous labor; cervical dilatation ≤4cm and no contraindications for vaginal delivery. Methods: Women were randomized into two groups A and B of 250 each, active phase considered at 4cm for group A and 6cm for group B. Labor duration was calculated and average labor curves were drawn. Main Outcome: To study the average labor pattern curve. Results: Mean duration of active phase from 4- 10 cm is 5.12±2.01 hours and from 6-10 cm is 2.79 ± 1.72 hours. 95th percentile values suggest that it took 5-6hours in progression from 4-6 cm and again 5-6 hours from 6-10cm. The minimum labor progression rate can be as low as 0.5cm/hour, still vaginal delivery can be achieved. The slope of labor curve steeps after 6cm, suggesting 6cm as the onset of active phase. Conclusion: Allowing labor to continue for a longer period before 6 cm of cervical dilation may reduce the rate of unnecessary intrapartum intervention and caesarean section for labor dystocia. Large-scale studies further needed for standardization of cutoff values for differentiating normal from abnormal labor. Funding: We received no financial support for the research, authorship, and/or publication of this article. Keywords: labor duration, nulliparous women, labor pattern, active phase of labor