I try to do at least 8-10 miles a week. (how long this takes me is quite different now than it was a few months ago... LOL!)
With the gestational diabetes, it's especially important for me. If I do not walk after every meal, my sugars are too high.
I'm very VERY strict with it. At night, while watching TV with my husband before bed, I walk in place for at least 20-30 minutes. If it's raining then during the day I may just pace back and forth in the house, walk in place.
I have found it helps me feel MUCH better pregnancy-wise. (obviously it goes without saying that this would not be the case with anyone having a different type of complication). If I skip even ONE day, I feel much slouchyer (lol, I sure doubt that one is a word) the next day.
I'm not sure if it's preparing me for labor, but it's definitely helping my pregnancy in general.
I have learned that I had to slow down on other things though, especially recently. I live on a farm, and hauling water buckets, restocking feed, things that involve lifting or pulling, are not longer on the activity list.
But walking... while it makes my legs tired and my feet hurt, definitely makes me feel better in general.