Exercise will boost your immune system and provide the circulation and energy levels needed to help you conceive. It will also keep you at a healthy weight, which can increase your chances of having a baby.

You don't have to be super fit, but it's important that you can easily climb the stairs, lift a reasonable weight, and not get too puffed out when you're chasing after a non-stop toddler. After all, you're planning to have a baby, and you'll need to be able to do all of these things when he or she arrives.

You'll be carrying around an extra two stone on average, so your posture and muscles will be under strain - and then, right at the end when you're exhausted - you have to go through the marathon of childbirth. Research shows that the anatomical changes of pregnancy put you at risk for muscle injuries in your lower back, hips and legs: 'Pregnant women risk overuse injuries just like athletes who throw a ball too many times, or who repeatedly swing a racquet,' says a study published in The Journal of Bone and Joint Surgery - so get training.

Can you be too fit to conceive?

Studies in the 1980s found that exercise might repress ovulation, but as one of the leading researchers in the field of pregnancy fitness, points out, the intensity of the exercise carried out in the studies was unusual. He concludes that, 'most healthy women can exercise vigorously without it affecting their fertility.' So there's no excuse not to get fit!

Why it's great to be fit now you're pregnant...

•  You'll improve your circulation and beat minor complications
As the mother and baby's circulation is inter-related through the placenta, anything affecting the mother's circulation can also affect the foetus. So good circulation is good for your baby, supplying her with more oxygen and nutrients via the placenta.

Improved circulation will also help to reduce the incidence of piles, varicose veins, swelling, cramps and constipation. In fact, exercise is a great way to beat the minor complications of pregnancy.

•  Improved posture and less backache
The weight of the baby alters your centre of gravity when you are pregnant and this combined with the effects of relaxin on ligaments can lead to bad posture, and backache.

A good antenatal class will continually reinforce the importance of good posture. Strengthening abdominal and back muscles will improve posture and also greatly improve your chances of avoiding backache. See the three key exercises to do now you're pregnant.

•  You'll be in a better state of mind
Pregnant women are more exposed to stress than ever before, and researchers have found that stress can increase your chances of having a premature baby. The good news is, that exercise releases the feelgood hormones, endorphins into the system. Add to that the physical benefits - better body shape and definition, better complexion - and you will certainly feel more positive and strong, and happy about being pregnant.

•  Reduce the risk of miscarriage
If you keep active you can reduce your risk of miscarriage by 40%, say researchers at New York's Columbia University. You don't have to be a slave to the gym. The researchers say being active includes doing the housework, walking or chasing around after young children. Remember that you should contact your GP if you have had more than one miscarriage before embarking on an exercise programme in pregnancy.

•  Exercise helps control high blood pressure
American researchers found that moderate exercise, such as walking or cycling, can help prevent pregnancy-related high blood pressure. The study looked at 16 women with a personal or family history of hypertension. At 14 weeks into pregnancy, the women were split into two groups; exercisers and no activity. After 10 weeks, the exercisers had a decline in diastolic blood pressure, while the no activity group's pressure went up. But remember that if you have pregnancy related high blood pressure you need to check with your GP if you can exercise.

•  You'll have a better birth
Scared about giving birth? You're not alone, but the good news is that the better your cardio vascular system (your heart and lungs) the more stamina you'll have for huffing and puffing your way through labour. Improved muscular strength will help you maintain positions like squatting during labour. Women who exercise are less likely to have a Cesearean or episiotomy, or go into premature labour. It is the amount of exercise in late pregnancy that helps. It takes a lot to achieve this benefit, ie, a moderate intensity at 40 to 60 minutes, five times a week.

•  You'll have a healthier placenta
Exercise helps you grow a bigger placenta, which is good news for your baby, as the placenta is the baby's substitute lung, kidney and liver, and transfers oxygen and nutrients to him/her.

A US researcher found that when women exercised, the placenta grew almost a third faster in mid-pregnancy, and had about 15% more blood vessels and surface area at term.

•  You'll produce a bigger baby
Researchers from the Department of Obstetrics and Gynaecology in Cleveland, Ohio, found that women who exercised 3-5 times a week had babies that were heavier, longer, and had better overall weight and body fat than those born to mums who hadn't exercised.

The study also found that the offspring of exercising mothers stay leaner at five years of age. The bigger babies were due to the spurt in placental growth, promoted by exercise. Is bigger better? Yes, apparently so. Another piece of research in the British Medical Journal found that the bigger the baby, the better the exam results.

•  You'll give your baby a head start
Want a happier, more intelligent baby? Exercise might help.

A study in the American Journal of Obstetrics and Gynaecology compared the newborn babies of women who exercised no more than once a week to the infants of mothers who'd run, swam, used stair climbers or done aerobics three or more times a week for at least 20 minutes. Five days after the birth, babies born to active mums were more alert and less fussy, suggesting that their mother's exercise may have given newborns a developmental boost.