Is it safe? Yoga is one of the most beneficial workouts you can do during pregnancy because of its emphasis on pelvic floor and core muscles. Yogic breathing techniques also come in handy during labor.
Altering your routine: In general, you should get in and out of postures slowly, to avoid sudden shifts in blood pressure and to accommodate your changing center of gravity. Steer clear of super stretchy positions, and after the first trimester, avoid lying on your back for more than a few minutes, as this can compromise blood flow to the baby. Skip face-down poses once your growing tummy makes them impractical. There are many yoga classes and videos tailored specifically for pregnant women -- if you're committed to continuing yoga through your pregnancy, consider one of these.
Is it safe? Pilates can give you some much needed core strength and help you maintain good posture as you grow larger, so I'm giving it a "yes," with alterations to the typical routine.
Altering your routine: Once you pass the three-month mark, many signature Pilates moves must be modified so they don't involve lying on your back. For seated poses, use a foam wedge or pillows for support. Extreme positions are a no-no -- they can leave joints chronically overstretched even after you've given birth. Breathing, always essential in Pilates, is even more important when you're growing a baby, to avoid blood pressure spikes, lightheadedness and dizziness. Best bet: Find a class or video that's specifically designed for pregnant women.