Walking is a great low impact exercise.
Although pregnant women may need to stop some of their other exercise activities, many walk right up to their delivery day.
If you are a runner, you might consider slowly switching to walking as your pregnancy advances as running is particularly hard on the back and knees for pregnantwomen.
Run-walk routines are pretty popular, where you alternate running with walking.
It is harder to walk when you're pregnant as you've quickly gained some weight and your center of balance has changed.
Make sure you walk in a natural position, standing tall and with your shoulders back, not hunched over as that increases the likelihood of back pain.
Since your center of balance is different, you probably want to avoid rough and uneven terrain, perhaps steep hills, and certainly slippery conditions like snow or ice covered ground.
If it's hot or humid you may overheat quickly as you now have the body heat of two.
If it's uncomfortable or treacherous walking outside, you may consider walking inside, for example at a mall or on a treadmill.
Be aware that treadmills require more balance than walking on the ground so you may want to use the handrails, not with a death grip but with a moderately firm stabilizing grip.
You may also want new shoes to walk in.
Not only may you want more shock absorbent shoes, or perhaps a new pair instead of your worn pair, but your foot size may increase from swelling.
Walking is an activity many women can continue throughout pregnancy.
Although other exercises may need to be modified or temporarily discontinued, you can feel good about walking, with your doctors permission of course!