Old Habit: Forgoing fish
Why it's bad: Yes, some seafood contains mercury, which can cross the placenta and harm your baby. But mercury-phobia can rob you of the benefits of fish and shellfish, which are low in saturated fat and contain high-quality protein. Not to mention omega-3 fatty acids, which can boost baby's brainpower and vision, and even help prevent postpartum depression, studies show. An added bonus: A small-scale study published in the American Journal of Clinical Nutrition found that higher levels of DHA (a type of omega-3) in the mother's blood correlated with better sleeping patterns in her newborn.
New healthy habit: Avoid eating shark, swordfish, king mackerel or tilefish. Instead, enjoy up to 12 ounces (two average meals) a week of a variety of fish and shellfish that are lower in mercury, such as wild Pacific salmon and tilapia, or ask your doctor about taking an omega-3 supplement.
Old Habit: Not drinking enough water
Why it's bad: Your blood volume nearly doubles by the third trimester, so you need plenty of water to help create it. Poor fluid intake can lead to lightheadedness and fainting, and dehydration can land you in the hospital facing serious consequences, including abnormally low amniotic-fluid levels and preterm labor.
New healthy habit: Slayton recommends drinking at least eight 8-ounce glasses of water a day. "Pale and plentiful urine is the key that signifies you're drinking enough]," she says. To stay hydrated, try keeping bottles of water with you at all times, and make deals with yourself throughout the day: You won't go to lunch until you finish a bottle; you have to polish off a bottle before your afternoon meeting is over. You get the drift.