Finding out you're pregnant needn’t mean giving up the things you enjoy. If you’re lucky, you’ll feel at your healthiest and if not, exercise may help by boosting your energy levels as well as your immune system.

Exercise builds muscle tone, strength and stamina, which can help your body cope with pregnancy weight gain (12.7kg, or two stones, on average). Exercise can also make it easier to regain pre-pregnancy fitness levels after the birth, and can help offset constipation, tiredness and circulation problems.

Try to keep active on a daily basis. Building in half an hour of activities like walking can help to keep you active. If you can't manage that, any amount is better than nothing.

General dos and don’ts

• Do remember that the appropriate level of exercise will depend on how fit you were before becoming pregnant.
• Do wear loose, comfortable clothes. Drink plenty of fluids and don't allow yourself to get overheated as this can be harmful to the baby.
• Do take a gentle approach to exercises that put strain on joints and ligaments. During pregnancy women are more vulnerable to joint and ligament injury because the body produces relaxin, a hormone which loosens joints and ligaments in preparation for childbirth.
• Do listen to your body. Dizziness and fatigue is not uncommon in the first 12 weeks or so, and some women lose their balance later on as the baby grows and their centre of gravity shifts. Stop and consult your health care provider if you experience vaginal bleeding, shortness of breath, palpitations (faster heartbeat) or pain in the back or pelvis.
• Do avoid contact sports and any activity with a potential for hard falls, such as horse riding.
• Don’t exercise in order to lose weight during pregnancy as this may harm your baby.
• Don’t exercise flat on your back, particularly after 16 weeks, as your bump presses on the big blood vessels and can make you feel faint.
• Don't use saunas or steam rooms. They can make you too hot, which can be harmful to the baby.

If you can’t talk easily while exercising, you’re overdoing it, so slow down. 

Yoga

Benefits Yoga is great for working your muscles without too much impact on your joints. Most of the breathing techniques used in yoga are a good preparation for childbirth, helping you to remain calm and breathe steadily through contractions. Yoga also improves posture, which will help with back pain and can increase flexibility, to make birthing positions such as squatting easier.

Considerations Some positions and breathing exercises will not be appropriate in pregnancy. Choose a qualified yoga teacher and always tell your teacher you're pregnant and, ideally, find a specialist pregnancy yoga class.

Stages of pregnancy This isn’t the time to try new and advanced poses. Focus instead on improving your technique. Bear in mind that as you move into the middle months and your baby grows, your centre of gravity shifts and you're more likely to lose your balance so sink slowly into yoga positions.

If you need to, use support such as a wall or chair for standing postures.

Running

Benefits For an experienced runner there are many benefits from running during pregnancy. It's an unbeatable cardiovascular workout which can be as long or as short as you can manage. But pregnancy is not the time to start running; walking is a safer option.

Considerations Running can be tough on joints and with the hormone relaxin loosening your joints there is a greater chance of injury. Wear supportive shoes.

Stages of pregnancy Drink lots of water and don’t run in the heat, especially in the first 12 weeks as overheating is potentially harmful to your baby. As your balance is affected by your changing centre of gravity, run on even ground.

In weeks 13 to 28 you may feel at your most energetic, but it's time to take less intense runs and more care as your pregnancy progresses. Consider a shift to swimming or walking in the last three months.

Walking
Walking is a safer option if you're not used to running. A brisk mile-long walk three times a week can help keep you fit and the fresh air might help combat morning sickness. Take the same precautions as running:

• Wear supportive shoes.
• Stay on ground that is level.
• Don't walk during the hottest part of the day.
• Carry water with you and drink it regularly.

The gym: aerobics and weights

Benefits Aerobics is great for the heart and lungs as well as improving muscle tone. As long as you stick to low-impact routines, you should be able to continue for as long as you feel able.

Always tell your instructor that you're pregnant or, better still, find a class for pregnant women.

Weight training improves muscle tone and builds stamina which will pay off during labour. In pregnancy, certain positions are not recommended so it's best to run through your routine with an expert first.

Considerations The main risk with aerobics and weights is putting too much strain on the joints, as they loosen during pregnancy. With care this can be avoided. You also need to be careful that you don't get too hot; if you feel hot, stop and rest.

Stages of pregnancy Avoid lifting weights while lying on your back after the first 12 weeks.

From week 13 or so, sit down to lift weights as long periods of standing in one position can lead to a drop in blood pressure and cause dizziness. Overheating can be a problem with aerobics so wear cool clothing and drink plenty of water. If you use a step in your routine, lower it or don't use it at all.

Avoid jumps (always keep one foot on the floor) and sudden changes in direction.

Swimming

Benefits Swimming has several benefits, from improved circulation and better muscle tone to increased endurance. Ideally, aim for 30 minutes, three to four times a week.

It's important to find a stroke that's comfortable for you and to avoid busy periods at the pool. Many pools run a range of antenatal swimming classes.

Stages of pregnancy As you move into your final three months the weightlessness that comes with water will be very comfortable, and you can continue swimming throughout pregnancy.

While other exercises involve an increased risk of injury due to the loosening of ligaments and joints in pregnancy, swimming doesn't as your body is supported by the water.


Taken from: http://www.nhs.uk/Livewell/pregnancy/Pages/Exerciseandpregnancy.aspx