When you're pregnant, you're constantly lifting weight, just walking around with a protruding belly. The simplest activities can already provide a workout. However, a new study says most pregnant women do not get nearly enough exercise.

According to a study by researchers at the University of North Carolina, Chapel Hill, only 23% of pregnant women get 30 minutes of exercise daily, the generally recommended amount. The American Congress of Obstetricians and Gynecologists (ACOG) and the Department of Health and Human Services both urge women with uncomplicated pregnancies to get 30 minutes of moderate exercise at least five days per week.

In the study, moderate intensity exercise was defined as exercise that caused light sweating, or a small rise in breathing and heart rate. Between 1999 and 2006, researchers surveyed 1,280 pregnant women, and found that more women did moderate to vigorous exercise during their first trimester as opposed to their third trimester. While 56% of them had engaged in some kind of exercise within one month of the survey, only 14% to 23% of pregnant women exercised regularly as recommended.

The benefits of regular exercise during pregnancy are nothing to dismiss. It leads to lower rates of depression, gestational diabetes and hypertension. Exercise can also help with body awareness, and ease any awkwardness you may feel walking around with a changing, ever-expanding physique. ACOG also says regular exercise can help prepare you for labor and delivery. Exercise boosts energy, aids sleep, and raises endurance while increasing muscle tone and strength. It also eases some of the more pesky ailments of pregnancy, like constipation, back pain, swelling, and moodiness.

Exercises such as swimming, cycling, brisk walking, and even aerobic classes are considered safe during pregnancy. However, it's essential to check with your health care provider before starting any exercise regimen, particularly if you want to take up a new exercise like running, weight training, or racquet sports. You might want to table your dreams of becoming a sports legend until after you've given birth.

Another study from researchers at the University of Auckland, New Zealand, found that women who exercise moderately during pregnancy give birth to slightly smaller babies, and these kids may have a reduced risk of becoming obese later in life. They studied 84 women pregnant with their first child. One group was tasked with doing moderate intensity exercises (riding stationary bikes) for 40 minutes, five times per week. The remaining women comprised the control group and went about their daily activities with no exercise regimen. The study followed everyone from week 20 through week 36, and all participants had a healthy body weight before the pregnancy.

At the end of the study, the exercise group gave birth to babies with a lower body weight and a lower body mass index — an average of 7.5 lbs compared to 7.8 lbs for babies born to sedentary mothers. Babies over 8.8 lbs are considered high birth weight. No differences were seen in baby length, length of pregnancy or the mother's weight.

If you want to know more about exercise during pregnancy, ACOG has a free patient education brochure available at ACOG.