This is an excellent question and one not without some measure of controversy. It has long been thought that walking during labor does help by shortening or speeding up labors. And this, from a common sense point of view seems to make sense, since the baby needs to descend through your pelvis, why not let gravity help, and the back-and-forth rocking motion of your hips when you walk would seem to help your pelvis open up and welcome the baby's descent. Contrary to this, when someone is having unwanted preterm contractions, it's long been noticed that exertional activities, such as walking, tend to be a problem and bedrest is often prescribed.

However, there was a recently published study that got a fair amount of press coverage that seemed to disprove the old adage that walking in labor is helpful. The authors compared two groups of ladies, some that had no restriction on their movement, and others that were kept in bed. When all other factors were held equal, there were no differences in the outcomes of their labor. The walking group seemed to be no better off.

At closer inspection though the study was, perhaps, flawed, since the ladies in the walking group were not encouraged to walk (just allowed to walk) and many did not do much of it.

My own take on the subject (unencumbered by the scientific method, but backed up by my wife who practically ran laps around our Labor and Delivery floor this past June) is that walking is indeed helpful. It only makes sense to me that being upright, and changing positions in general, seems to help speed up labors, to make you a bit more comfortable with contractions at times, and probably helps the baby descend and rotate into just the right position for delivery.