What to avoid

A pregnant woman's heart is working 50% harder than normal .

While most exercises are safe, certain ones like rollerblading, scuba diving, horse-riding, racquet sports which require rapid movements such as squash and tennis, and contact sports such as hockey and soccer, should be avoided.

Pregnant women should also avoid activities which involve extreme stretching, bouncing or jumping because relaxin, a hormone produced during pregnancy, makes their ligaments and joints softer and more lax.

This condition increases their risk of strains and sprains.

Muscle cramps are common in pregnancy even without exercise as mineral depletion can occur so maintaining dietary intake of calcium, magnesium, salt and potassium is important.

Pregnant women who experience symptoms like dizziness, faintness, excessive aches and pain, vaginal bleeding, excessive shortness of breath before or during exertion, calf pain or swelling, painful uterine contractions or decreased foetal movement, should stop exercising and consult their doctor.

What is safe

FIRST TRIMESTER: Exercises like walking, running, moderate intensity aerobics, cycling, swimming and dancing are good to start with, according to Dr Choo Wan Ling, a consultant obstetrician and gynaecologist at Pacific Healthcare Specialist Centre.

Dr Anne Hagarty, a consultant obstetrician and gynaecologist at Mount Elizabeth Hospital, said: "The emphasis is on low-impact activities and maintaining a heart rate of below 140."

SECOND TRIMESTER: Most women in their second trimester can continue or start doing exercises like pre-natal yoga, brisk walking and swimming.

Dr Ho Hon Kwok, a consultant obstetrician and gynaecologist at H K Ho Women & Fertility Clinic at Mount Alvernia Medical Centre, said: "For cycling, the growing belly can affect your balance and make you prone to falls. You may want to stick with stationary biking in the later stages."

He added that after the first trimester, women should not do exercises that require them to lie flat on their backs as this could increase their risk of low blood pressure.

Dr Choo said: "Gym training is beneficial. It would be good to work on your butt and leg muscles as they have to cope with increasing weight during the pregnancy."

THIRD TRIMESTER: Pregnant women should wind down the intensity of their exercise. Brisk walking and swimming are good ways of relieving back pain and improving cardiovascular fitness.

Dr Choo said: "As more blood needs to be channelled to the growing baby, less blood or oxygen is available for your muscles and heart. Your heart is already working 50 per cent harder so what you need is just some light exercise to keep your body active."

This article was first published in Mind Your Body, The Straits Times.