This is actually pretty much the same as I was told by my dr. when I was pregnant 16 years ago (my how time flies when you're having fun).
Don't overheat, don't raise your heartrate to extreme levels, don't take up new sports that require good balance, but by all means keep doing things you're proficient in. I happily kept on cycling, hiking, skiing and rock climbing, though the latter on top-rope, throughout my pregnancy. My greatest concern was injuries caused by loosening joints, and the greatest problem I actually had was: ack, no lungs! all squashed together in there!
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I'm glad to hear this is official advice now. I got a bit tired of nosy lay-people hinting that I should be sitting on the couch crocheting instead.
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett