BODY WATCH : When You’re Eating for Two, How Much Is <i> Too </i> Much?

Call it the tightrope act of pregnancy.

Gain too little, you risk the baby’s health. Gain too much, you will never zip those jeans again.

In years past, the “ideal” weight-gain recommendation has fluctuated. But since 1990, there has been a consensus, based on research, that takes into account individual differences.

In general, a woman of normal weight before becoming pregnant should gain about 30 pounds, according to guidelines adopted by the American College of Obstetricians and Gynecologists (ACOG). Underweight women can gain about 34 and obese women about 20; women carrying twins are allowed 40.

But among veteran obstetricians, there’s leeway.

“I recommend 25 or 30 pounds for a single pregnancy, 35 to 40 for twins,” says Dr. Arthur Wisot, a Torrance obstetrician/gynecologist. “The window of normal can be 20 to 35.”

Ideally, the weight gain should be slow and steady. “But it’s not exactly linear,” says Dr. Roy Pitkin, UCLA professor of obstetrics/gynecology. During the second trimester, the period of much fat storage, it’s not unusual for a woman to put on eight or 10 pounds in a month, he says.

So where does that 30 pounds, give or take, go? The baby makes up about 7 1/2 pounds, according to ACOG. Amniotic fluid adds two; breasts, two; uterus, two; increased blood volume, four; increased fluid volume, four; maternal stores of fat and nutrients, seven; placenta, 1 1/2.

Gaining too much is the problem for many women, as L.A. attorney Stacey Bieber, 28 and pregnant with her second child, knows. She gained 50 pounds with her first and wants to do better this time. At 18 weeks, she’s gained 12 pounds--a bit more than she’d hoped, but she’s still motivated.

Netty Levine, her dietitian at Cedars-Sinai Medical Center, offers these tips: Avoid regular soda to reduce calories; minimize drinking of juices, which are relatively high-calorie; plan meals; don’t skip meals.