My wife and I just had a baby so I can speak to this a little. Our baby was 10lbs and when she came out she damaged my wife quite a bit.  Enough where we needed to go to the hospital for stitches. The midwife made it clear that if my wife worked out and moved more during pregnancy that our baby statistically would have been a normal weight and size and thus easier to give birth to without complications. 

Note that my wife was pretty much incapacitated during the whole pregnancy and could not move much.

Hope this provides one data point for you. 

My wife and I just had a baby so I can speak to this a little. Our baby was 10lbs and when she came out she damaged my wife quite a bit.  Enough where we needed to go to the hospital for stitches. The midwife made it clear that if my wife worked out and moved more during pregnancy that our baby statistically would have been a normal weight and size and thus easier to give birth to without complications.

That matches what I've read about strength training helping to prevent gestational diabetes.  That would make it a great benefit to mother and child.

I'm long past my child-bearing years, but I do strength training.  It is supposed to help with many conditions associated with aging and I am hoping to avoid being a burden on my family.  I can't say for sure, but this may be why I am one of the minority of people my age who is not on medication.

Your body pushes the baby out for you. If you force it, you risk tearing. Also some birthing positions can help open up the pelvis like being upright. I think endurance and mental fortitude are more important. And of course being in a stress-free environment.