As you’re probably well aware, between hormones and physical changes, pregnancy can make you really tired during the day -- especially during your first and third trimesters. “Yes, it’s okay to nap,” says Ana-Maria Gallo, Ph.D., R.N.C., director of nursing education, research and professional development at Sharp Groffmont Hospital in San Diego. “But keep it to less than 40 minutes; any more and you’ll throw off your circadian rhythms (a.k.a. your internal body clock), making it difficult and even impossible to fall asleep at night,” she says. If you’re sleepy after 4 p.m., skip the nap and plan to hit the sack early instead.