4. Calling it Quits. When it comes to pregnant runners, some women, like my OB, pretty much jog into the hospital, time their contractions with a Garmin, and pop out a baby with some Adidas on their feet. Other women, like me, call it quits way before they deliver the baby. I made it to 30 weeks during my pregnancy with Maggie.
Moms-to-be hang up their shoes for all kinds of reasons (pants peeing, straight up tiredness, aches and pains, can no longer wiggle into spandex, etc), and any of those reasons are fine. If you feel like stopping, stop. Pregnancy is unpredictable, so telling yourself, "I'll run until I'm 37 weeks!" when you're 6 along weeks is totally unfair to you. Play it by ear. You're not running against anyone else.
I stopped for 2 reasons. First, I was getting ginormously huge and my shorts were turning into something like a strange scene out of a niche-porn movie. And second, I had a wicked case of public symphisis diastisis that honestly left me feeling like I was stabbed after every run. Not worth it in my book.
5. Avoid Injuries. When you're running pregnant, you're a lot more susceptible to sprain and strain injuries. The extra relaxin pumping through your body loosens up the ligaments and leaves you a lot more likely to mess up a joint. Be sure you really watch your footing, run on even surfaces (like well maintained roads, or the treadmill), and avoid gnarly trails all together.
6. Be Safe. As a pregnant runner, always always always carry a cell phone. I don't care if you're running half a mile out and half a mile back, carry your cell phone. If you're running, have a cell phone on you. Oh, and make sure you carry your cell phone. You never know when you might tweak a joint, or feel a little light headed, or just want to go to McDonalds for one of those hot fudge sundaes immediately. You'll definitely need a cell phone to address any of those situations. So carry your cell phone.