After seeing a positive sign on a pregnancy test, some women might want to plan repeated dates with Ben & Jerry's ice cream.

Sure, getting plenty of rest is important when expecting, but does a new pregnancy really mean a woman has a license to let her sneakers collect dust for the next nine months?

According to Dr. Linda M. Szymanski, a fellow in maternal-fetal medicine at Johns Hopkins University in Baltimore, fewer than 16 percent of pregnant women are physically active enough to meet current recommendations and 23 percent of previously active women stop exercising altogether.

While some of these mamas-to-be might have complications that require them to do little more than couch surf, it is safe for most women to exercise throughout pregnancy.

Being active has multiple advantages for both mother and child.

The main concern for all pregnant women is the baby's health, said Peg Moline, editor in chief of the magazine Fit Pregnancy. "But there is no evidence that moderate prenatal exercise can cause miscarriage, and the many benefits include elevated energy levels, achieving a reasonable pregnancy weight at a reasonable rate, and increased stamina, which might help speed up the labor process or at least help a woman endure it," she said.

Another important benefit is a decreased risk of developing gestational diabetes. Babies born to mothers with diabetes are significantly more likely to have problems both at delivery (larger size, increased risk of shoulder dystocia) and later in life (childhood obesity, type 2 diabetes), Szymanski said. To prevent these outcomes, the American Diabetes Association has endorsed exercise as a helpful adjunctive therapy for gestational diabetes.

Small studies also have suggested a reduction in pre-eclampsia in women who participate in regular physical activity during the first 20 weeks of pregnancy, Szymanski said. And research shows that active expectant mothers are more likely to continue their program after the baby is born, which can assist in speedy postpartum weight loss, fewer muscle and bone problems such as back pain, and decreased incidence of postpartum depression.

If you're sold on working up a sweat but are currently sedentary, Syzmanski advised gradually building up to 30 minutes of moderate exercise (for example, walking briskly but able to maintain normal conversation) a day, up to about five days per week. Women who frequently exercised before pregnancy typically can continue a similar routine, as long as it continues to feel comfortable.

Need advice on what activities work best for growing bellies and loosening ligaments? Moline recommended walking (which also can help quell nausea), swimming and prenatal yoga classes that are specifically designed to address issues expecting moms might be experiencing. They also need to avoid potentially unsafe poses.

"Weight lifting and other forms of strength training are also important for maintaining muscle tone," Moline said.

As for activities to ditch, "use common sense," Syzmanski said.

In other words, steer clear of contact sports such as ice hockey, basketball or rugby, or pastimes that have a higher risk of falling, such as horseback riding, gymnastics or skiing.

Many medical professionals also will suggest that pregnant women avoid exercise that necessitates lying on the back after the first trimester, as the increased weight of the uterus could interfere with the flow of blood and nutrients to the placenta and the baby. But Syzmanski usually tells women that this advice applies to prolonged periods of lying on the back, not brief sessions.

Either way, it's essential to listen to the body. Stop exercising and contact a doctor if you experience problems, such as vaginal bleeding, shortness of breath while at rest, dizziness, headache, chest pain, muscle weakness, calf pain or swelling, preterm labor, decreased fetal movement or amniotic fluid leakage.

To help prevent such problems, drink plenty of water before, during and after a workout, and take it easy (or take a workout indoors) when it's hot outside, Moline said.

"And you never want to push yourself to go harder or longer than you did before pregnancy," she said.