Exercise in Pregnancy

Pregnancy used to spell the end of a woman's sporting career but in recent years many great female athletes have returned to their sport and competed at the highest level.
How will pregnancy affect performance?
Increase in body weight at an average of 10-15kg.  This has an effect on the body shape as weight is distributed in different areas.  In turn changing the centre of gravity which will result in extra curvature of the spine.
Loosening of all ligaments.
Caused by the hormone relaxin your joints will gradually loosen up.  This Crete's an increased injury risk. 
Increase in resting heart rate.
Due to the increase in resting and decrease in maximal HR it is not recommended using target heart rates to determine intensity in exercise.  This is best monitored by the mothers symptoms of exertion.  it is recommended you consult your doctor when assessing your your intensity.  She should stop when fatigued  and not exercise to exhaustion. 
If using a HR to determine intensity, guidelines advise 140BPM.  This however is not an absolute.  A HR of 150-160 is reasonable for an active woman as long as no adverse symptoms are evident.
Decrease in Blood Pressure
During trimester 2, the development of blood vessels to supply the growing placenta will cause blood pressure to fall.  Spells of dizziness can prevail from sudden movements from lying to standing etc.  After month 4 lying on back exercises should be avoided due to weight of the foetus impeding on the return of blood to the heart.
Pelvic Floor
Damage to the pelvic floor muscles occur during birth.  The pelvic floor muscles are weakened during pregnancy so it is extremely important to begin conditioning of the these muscles from the outset.  Seek advice from your physio.  Persistent training of these muscles can help prevent bladder control problems and exercise related incontinence.
Are there any dangers of exercise during pregnancy?
Main concerns are

• Over heating-avoid hot and humid conditions, poor ventilation.  Use breathable clothing and special attention to fluid replacement
• Impairment of oxygen
• nutrient delivery to the foetus
• possible risk of premature delivery

Risks to mother
Pregnant women undergo many changes that have the potential to increase risks of injury.  Postural changes increasing lordosis, a shift in the centre of gravity and well as weight gain.  Particularly in the 2nd tri these can alter balance and co ordination.
A change in hormonal levels aid in the relaxation and mobilisation of pelvic joints and can cause problems with instability and injury in the sacroilliac and pubic symphysis joints.  Avoid excessive stretching and ballistic movements.
Precautions
Exercise should be stopped if any abnormal symptoms occur such as pain, bleeding, dizziness or unusual breathing.
Any exercise should not be undertaken without consulting your doctor or obsterician first.
Pregnancy is not the time to start a more intense exercise program but rather continue and modify an existing one.  Its a time for maintenance not reaching heights.
When can you resume after the baby is born.
After a normal delivery gentle exercises can resume once you are comfortable.  More intense exercise should be delayed for 6 weeks after consultation with your doctor.  C section delivery should be 6 weeks minimum as long a wound has healed.
Please stop if you experience any of the following

• High HR
• Dizziness
• Headache
• Uterine Contractions
• Vaginal bleeding
• Amniotic fluid leakage
• Nausea
• Insufficient weight gain
• Shortness of breath
• Back or pelvic pain
• Decreased foetal movement
• Sudden swelling of ankles, hands or face.

Sports medicine Australia
Women in sport-fact sheet 2