The bird flu hasn't gotten us yet, but our nation is clearly suffering from the Great Sedentariness Pandemic of 2005 -- a virulent condition whose symptoms include watching television, working at a computer, commuting by car and growing out of a favorite pair of jeans. This week we bring the sobering news that the illness is passing to the next generation in utero.

Only 16 to 19 percent of healthy pregnant women get the recommended levels of exercise, according to a study published in the October issue of Medicine & Science in Sport & Exercise. This is even worse than the lousy exercise compliance rate for all women in the study, 27 percent.

Healthy women with no unusual risk factors and an uncomplicated pregnancy should get the same level of activity as the rest of us: 30 minutes of moderate activity most days of the week, according to the American College of Obstetricians and Gynecologists (ACOG).

Sedentary pregnant women may face a higher risk of gestational diabetes and excess weight gain than those who are active. They may suffer more aches and pains, including backache. Exercise can help control depression, including the post-partum variety; it can also strengthen bones, joints and muscles to prepare for the Ironwoman event they call delivery.

While the research record is not as clear, it appears that the general benefits of a mother's good health convey to the fetus. In any event, for healthy pregnant women who consult with their doctors, there is no risk to the baby from moderate, no-contact exercise.

Researchers in the current study mined data from 150,259 women age 18 to 44; of those, 6,528 were pregnant. In almost all modes of exercise, non-pregnant women reported a higher participation than did pregnant subjects.

Two exceptions were walking -- 52 percent of pregnant women reported walking for exercise, compared with 45 percent of non-pregnant women -- and swimming (4 percent and 3 percent, respectively). ACOG recommends that pregnant women avoid scuba diving, contact sports or other exercises that might cause abdominal distress.

Walking makes sense as an activity for pregnancy: it is fairly low impact, highly accessible and easier to schedule than most activities. Water-based workouts might be even more appealing, especially during the third trimester: You feel lighter, have much lower risk of a fetus-damaging fall and encounter almost no impact).

"Most pregnant women are pleasantly surprised" by water workouts, says Christelle McDonald, who teaches a prenatal aquatics class at the Bethesda-Chevy Chase YMCA. "You are so light [in the pool]. You can do a whole-body workout. For most women, the biggest apprehension is getting into a bathing suit. Once they're in the water, it's hard to get them out." McDonald describes her 75-minute sessions as "a gentle water aerobics class," in which she uses "bigger, slower" moves than those in typical aquaerobics.

During the second and third trimesters, women should avoid exercise that involves lying on their backs: That could compress the inferior vena cava blood vessel, limiting blood flow to the fetus. This applies to certain moves in weight training, yoga and Pilates. Women participating in any of these should locate classes or trainers specializing in exercise for pregnancy.

And of course: No pregnant woman should begin, or continue, an exercise program without consulting her ob/gyn.

We are not pregnant (thanks for asking; it's just the post-Thanksgiving belly you see). But we will be online today, 11 a.m. to noon, for our biweekly fitness chat at www.washingtonpost.com.

-- John Briley

Exercising while expecting may boost mood, lower disease risk and help you prepare for delivery.