A Nice, Fat Brain
By the middle of the second trimester, the fetus's main work is to grow a bigger body and brain. "Fetal brain cells at six months are like saplings -- tiny little branches," says Eliot. "As they massively move out, a child's brain turns on."
To build the brain, fetuses and babies need many things, including a unique kind of fat called docosahexaenoic acid (DHA), an omega-3 fatty acid found primarily in fish. Not only does DHA help grow the branchlike dendrites, but it's also an essential component of myelin, an insulating sheath around nerve cells. "Myelin speeds up the rate at which our brains process information -- it's like going from a 486 to a Pentium 4," says Eliot.
"The brain triples or quadruples during the third trimester, and these fatty acids are uniquely concentrated in the brain during that period," says William Connor, M.D., professor of medicine and clinical nutrition at Oregon Health Sciences University. Experts recommend that pregnant women eat two servings of fish a week, including one fatty fish like salmon; vegetarians should cook with canola, flaxseed, or walnut oil; and anyone who can't do either should take a daily supplement containing one or two grams of omega-3 fatty acids.
You've finally reached the end of your pregnancy, and you're ready. How big will the baby be? How much will it weigh? You can think of the ideal as the Goldilocks standard: not too big, not too small.
An optimal birth weight, it's now thought, may set the stage not just for a healthier baby but for a healthier child and adult. Low-birth-weight babies -- those born at under five and a half pounds -- are at risk for many problems, immediate and long-term. But those born at over nine and a half pounds also risk being overweight as a child and an adult, says Mary Cogswell, a nurse-epidemiologist in the Maternal and Child Nutrition Branch of the Centers for Disease Control and Prevention, in Atlanta. Some of the risk may stem from having an overweight mother, researchers believe.
Prevention isn't simple, although gaining an appropriate amount of weight during pregnancy is part of the answer. Women who gain too much -- and 40 percent of pregnant American women do -- are more likely to have a too-heavy baby and to remain overweight themselves after giving birth. Excess weight gain also increases the risk of gestational diabetes, which ups a woman's chance of delivering a too-large infant. As obesity rates have risen over the past 20 years, so have rates of diabetes.
To gain 25 to 35 pounds during pregnancy, you need only about 300 extra calories a day. That's the equivalent of three extra glasses of skim milk. "Strive for a variety of fruits, vegetables, whole grains, dairy, and protein," says Tufts University nutrition professor Susan Roberts, Ph.D., coauthor of Feeding Your Child for Lifelong Health. "Limit unhealthy foods that encourage excess weight gain."