- If you've had a baby before (parity)
- Your pelvis (shape and size)
- Your baby's position
- Contraction strength and timing
- Natural labor or induction
First time moms were reported generally to see the first stage of labor last about 6-12 hours from the time they are four centimeters, average was 7.7 hours. The longer labors were just over 17 hours. Second (or more) time moms reported average in older data was 5.6 hours. On the long end, second moms were near the 14 hour mark. This is based on data from the 1960s.
The World Health Organization (WHO) recommends that once you hit the four hour mark in the second stage (pushing) that intervention be considered.
You might be thinking that this doesn't sound at all like the length of labors that you have heard of from your friends. This is because so many people count labor very differently. That early labor is really something is not done in the hospital for many women, so it isn't really counted in many of the averages when looking at the length of labor.
Another factor to consider is that new research shows that labor is actually longer now than it was in the 1960s when most labor pattern data is taken from. So when you look at the numbers above, add 2.6 hours for a first time mother and about 2 hours for a mother who has had children before.
Laughon, S.K., Branch, D.W., Beaver, J., Zhang, J., Changes in labor patterns over 50 years, American Journal of Obstetrics and Gynecology (2012), doi: 10.1016/j.ajog.2012.03.003.
Myles Textbook for Midwives. Fraser, D, Cooper, M. Fifteenth Edition.