Not so long ago, women were advised to take it easy and rest during pregnancy. But in recent years, there's been increasing scientific evidence on the benefits of physical exercise. "Physically active women experience fewer complications of pregnancy such as gestational diabetes, hypertensive disorders and low back pain, to name a few," according to fellows from the American College of Sports Medicine writing in the July/August 2013 issue of Current Sports Medicine Reports . They encourage women having uncomplicated pregnancies to achieve a minimum of 150 minutes of moderate-intensity physical activity a week, and encourage physicians to counsel women to exercise regularly during pregnancy. "A majority of women do not meet the recommended levels of physical activity before and during pregnancy," they wrote. Guidelines from the Hong Kong College of Obstetricians and Gynaecologists recommend all pregnant women without contraindications to participate in aerobic and strength-conditioning exercises. "Performing regular mild to moderate exercise sessions, three or more times per week, is advisable," they say. Pregnant women who exercise tend to have a shorter delivery time and quicker recovery after giving birth, plus a lower risk of post-pregnancy obesity, says Emily Ko Ming-lai, a physiotherapist at Hong Kong Sanatorium and Hospital. "Exercise is also good for mood - it helps control antenatal and postnatal depression," says Ko. Just six months after giving birth, Rachel Isabel Yang returned to her pre-pregnancy shape and resumed competitive pole vaulting. She jogged and did weight training up to five months into her pregnancy, and thereafter did up to 60-minute sessions daily on a ski machine at home. "I had a very healthy pregnancy," says Yang, 31, a general manager whose baby is 10 months old. "I was happier and less tired compared to my peers who were also pregnant at the same time. Exercise definitely made my delivery easier; I spent 20 minutes pushing my baby out." Exercise does not lead to harm or risks for the fetus - and may even have a positive effect on fetal growth and adaptation, according to a systematic review of 19 recent randomised controlled trials on healthy pregnant women who underwent a physical exercise programme. The review was done by scientists from the University of Campinas in Brazil and published last year in Current Opinion in Obstetrics and Gynaecology . As little as 20 minutes of moderate exercise three times a week during pregnancy could enhance a newborn child's brain development, say University of Montreal researchers, who presented their study findings at the Neuroscience congress in San Diego last month. Another recent study, published in the journal Experimental Physiology , found that exercise during gestation is a powerful programming stimulus in the arteries of offspring that may affect the risk of future cardiovascular disease. The former study, however, was small - only 10 women were involved - and the latter study was conducted on pigs. Therefore, though available evidence suggests that there is no harm from exercise during pregnancy and potentially many benefits, "one of the main problems is that there are very few good quality studies on this topic", says Dr Marie Tarrant, associate professor at Hong Kong University's School of Nursing. Anecdotal evidence, however, is strong. "My pregnancy was an extremely easy one," says Shireen Shen Jega, 28, a part-time teacher and mother of a 15-month-old girl. "I had no morning sickness, was full of energy and had a fantastic appetite. I had a couple of aches here and there but nothing too serious." Jega attributes this to her regime of high-intensity interval training - a modified, shorter and low-impact version done three times a week - along with Pilates and yoga. Trina Foo-Crichton's labour took 44 hours, and she carried up to 14 kilograms of extra weight. "If I wasn't in shape, I would have found both much more difficult," says the mother of a 10-week-old baby. Her fitness regime consisted mostly of a modified version of Ashtanga yoga and long walks in the park. "The level and kind of exercise a pregnant woman can do safely really depends on how fit she is before pregnancy," says Tarrant. "Women who exercise regularly before pregnancy can generally continue exercising as previously, as long as they're not having complications such as spotting or bleeding. Women who were sedentary before pregnancy can do moderate exercise such as brisk walking, but shouldn't take on new or overly strenuous exercises during pregnancy." Ko advises that women who didn't exercise or are overweight before pregnancy start with 15 to 20 minutes of aerobic exercise three days a week. Extend workout time by only two minutes a week up to 40 minutes, then increase the number of days for a total of 150-160 minutes a week. Aerobic exercises such as brisk walking, running, using a treadmill or stationary bicycle, swimming and water aerobics are all recommended. Heart rate should be monitored during exercise, says Tarrant, and kept to about 60 to 80 per cent of one's maximum effort. This means you should be exercising "somewhat hard" but still be able to carry on a conversation. Lifting heavy weights should be avoided. Contact, high-impact or vigorous sports may involve the risk of abdominal trauma, falls or excessive joint stress. Trail running probably isn't a good idea, either. Erin Bowland, 34, a mother of two, had competed in trail running before pregnancy and tried to keep up the sport when carrying her first child. But at five months' pregnant, she tripped and fell onto her stomach. "Your co-ordination is compromised during pregnancy, and your ligaments are stretchy and not as stable as normal, so I realised it was too dangerous for me to try and navigate roots and rocks on trails," she says. "I stuck to road running instead after that little scare." The key in exercising is to listen to your body, pregnant or not, says Wong Ching-yee, 35, a communications manager who has a two-year-old girl. She swam and ran up until she was four months' pregnant, then replaced running with Pilates. "Sports is my form of therapy, so I'm grateful that I could continue swimming right until the very end of my pregnancy, otherwise I would end up as one very angsty mother," says Wong. email@example.com Safety considerations From the Canadian Society for Exercise Physiology. To find out if you're ready for exercise during pregnancy, do the society's PARmed-X quiz at parmedx.appspot.com 1. Avoid exercise in warm/humid environments, especially during the first trimester. 2. Avoid isometric exercise or straining while holding your breath. 3. Maintain adequate nutrition and hydration - drink liquids before and after exercise. 4. Avoid exercise while lying on your back past the fourth month of pregnancy. 5. Avoid activities which involve physical contact or danger of falling. 6. Know your limits - pregnancy is not a good time to train for athletic competition. 7. Know the reasons to stop exercise and consult a qualified health care provider immediately if they occur.