There are no data in humans to indicate that pregnant women should limit exercise intensity and lower target heart rates because of potential adverse effects. For women who do not have any additional risk factors for adverse maternal or perinatal outcome, the following recommendations may be made:

During pregnancy, women can continue to exercise and derive health benefits even from mild to moderate exercise routines. Regular exercise (at least three times per week) is preferable to intermittent activity.

Women should avoid exercise in the supine position [lying on the back] after the first trimester. Prolonged periods of motionless standing should also be avoided.

Women should be aware of the decreased oxygen available for aerobic exercise during pregnancy. They should be encouraged to modify the intensity of their exercise according to maternal symptoms. Pregnant women should stop exercising when fatigued and not exercise to exhaustion. Weight-bearing exercises may under some circumstances be continued at intensities similar to those prior to pregnancy throughout pregnancy. Non-weight bearing exercises such as cycling or swimming will minimize the risk of injury and facilitate the continuation of exercise during pregnancy.

Loss of balance could be detrimental to maternal or fetal well being, especially in the third trimester. Further, any type of exercise involving the potential for even mild abdominal trauma should be avoided.

Pregnancy requires an additional 300kcal/d in order to maintain metabolic homeostasis. Thus women who exercise during pregnancy should be particularly careful to ensure an adequate diet.

Pregnant women who exercise in the first trimester should augment heat dissipation by ensuring adequate hydration, appropriate clothing and optimal environmental surroundings during exercise.

Many of the physiologic and morphologic changes of pregnancy persist 4-6 weeks postpartum. Thus pre-pregnancy exercise routines should be resumed gradually based on a woman's physical capability.

Contraindications to Exercise

The aforementioned recommendations are intended for women who do not have any additional risk factors for adverse maternal or perinatal outcome. A number of medical and obstetric conditions may lead the obstetrician to recommend modifications of these principles. The following conditions should be considered contraindications to exercise during pregnancy:

• Pregnancy induced hypertension
• 
  
• Pre-term rupture of membranes, Pre-term labor during the prior or current
• 
  pregnancy or both
• Incompetent cervix/cerclage
• 
  
• Persistent second or third trimester bleeding
• 
  
• Intrauterine growth retardation
• 
  
• Multiple gestation

In addition women with certain other medical or obstetric conditions, including chronic hypertension or active thyroid, cardiac, vascular or pulmonary disease, should be evaluated carefully in order to determine whether an exercise program is appropriate.