Yes, I got the following advice from a pregnancy book. Still, the advice is relevant for anyone who has to sit for prolonged periods of time.

The authors of “What To Expect When You’re Expecting” state the following: “Sit smart. Sitting puts more stress on your spine than almost any other activity.” The authors state that it is advisable to use chairs that provide good back support, such as a straight back chair with firm cushioning. They also warn not to cross your legs because doing so can cause your pelvis to tilt forward, resulting in added pressure to strained back muscles.

Finally, “What To Expect When You’re Expecting” says: “Sitting for long periods can be as bad for your back as sitting the wrong way. Try not to sit for more than an hour without taking a walking and stretching break.”