Exercising during pregnancy can be beneficial for both mother and baby. Women's Editor Christen Pears talks to one mother-to-be who's a regular at the gym.

LISA Campbell's baby is due in nine weeks but she goes to the gym every day. She becomes tired more easily and she's cut back on the amount of exercise she does, but she still manages to do more than most non-pregnant women.

"A lot of women use being pregnant as an excuse to stop exercising altogether and eat rubbish but I'm hoping to exercise all the way through," she says.

"Before I was pregnant, I used to go to the gym for an hour to an hour-and-half every day. I've cut that down to about half an hour and I don't do anything as strenuous."

Lisa, who is 31, works out at Bannatyne's Health Club in Darlington, where she walks, cycles and uses the cross trainer. The instructors have drawn up a special programme and keep an eye on her to make sure she isn't overdoing it.

She says: "I think it's really important to keep exercising. It will help me get back into things once I've had the baby. I'm also hoping that it will build up my stamina for the birth.

"I'm actually having a water birth and all my colleagues have been joking that I'll be doing a couple of lengths while waiting for the baby to arrive. It is funny but there's also a serious side. You should try and keep fit while you're pregnant."

Corlette Boyle, health and fitness manager at Bannatyne's, recommends moderate physical activity for pregnant women.

"It will give the woman more energy, help her feel better physically and mentally and will improve sleeping. It strengthens muscles and increases endurance, which is very important during labour.

"Women who don't exercise during pregnancy become less fit. They become heavier and heavier and it's far more difficult for them to regain their shape after delivery."

A fitness instructor can devise an exercise programme that fits in with your lifestyle. Corlette recommends moderate aerobic exercise such as walking or cycling, although she stresses this should be on an exercise bike rather than outdoors because of the increased risks of falling. Swimming is also very good as the water takes the weight of the baby.

Expectant mothers should also try non-aerobic exercise. Yoga focuses on breathing and relaxation, also very helpful for during birth. Pilates strengthens the core muscles around the stomach and pelvis, and was one of the reasons celebrities including Catherine Zeta Jones and Liz Hurley managed to get back in shape so quickly after having their children. Some gyms and fitness centres run classes specially for pregnant women.

Weight training helps keep muscles toned, although Corlette recommends avoiding heavy weights and focusing on multiple repetitions.

She says: "It's best to exercise before you get pregnant. Most of the women who come to us are regulars and just want to carry on - but it's never too late to start. You just need to make sure you have the go-ahead from your doctor and take things slowly and gently at first until you can do 20 to 30 minutes four or five times a week.

"A lot of people don't realise they can exercise when they're pregnant. They it's some sort of disability but it isn't. It's very safe as long as you do it properly and you will certainly feel the benefits when you are pregnant and afterwards."

There are no specific guidelines about how long you should work out but you should be guided by your pre-pregnancy fitness regime. Experts advise keeping you heart rate at 65 to 70 per cent of maximum to prevent the baby from becoming too warm.

You should also take care when stretching. During pregnancy, the body produces more of the hormones that that loosen joints and ligaments, making them more prone to strain. You should not push your stretches too far as you can cause yourself permanent injury.

Dr Maggie Blott, consultant obstetrician at Newcastle's Royal Victoria Infirmary would encourage all pregnant women to do some form of exercise.

"If you've never exercised before, pregnancy isn't he best time to start a vigorous exercise programme but I would recommend doing something, even if it's just a 20-minute walk two or three times a week.

"It keeps your body supple. It keeps you fit and helps you cope during labour. You will also recover more quickly," she explains.

Putting on too much weight during pregnancy can lead to a higher risk of a Caesarian section and makes you more prone to diabetes and blood clots in the legs.

Swimming is particularly beneficial, as well as being safe. If you are already a regular gym-goer, you can ask your instructor to modify your programme so you can continue through your pregnancy.

There are, however, some activities that should be avoided.

Dr Blott says: "Snow and water ski-ing are not recommended after 12 weeks. You should also avoid horse riding because of the risk of falling and harming the baby, and scuba diving is not considered a good idea because no one knows the effect of increased water pressure."

As a general rule, she recommends continuing with your existing exercise but take into account any feelings of discomfort. Reduce your level of exercise if you feel hot or tired and always consult your GP or midwife.