EXERCISE AND PREGNANCY

The following article is based on the 2002 American College of Obstetricians and Gynecologists (ACOG) guidelines(1) and an article discussing these guidelines in the British Journal of Sports Medicine in 2003.(2)  These 2002 guidelines were intended to replace the 1994 ACOG guidelines. While the 1994 ACOG guidelines acknowledged that exercise can be safely continued during pregnancy, these new guidelines recommend exercise not only for those women who were already exercising, but also for sedentary women and even for those with medical conditions, like diabetes.  Sedentary pregnant women and those with medical conditions should be examined by their doctor before engaging in exercise.  

According to these 2002 ACOG guidelines, "Generally, participation in a wide range of recreational activities appears to be safe during pregnancy...In the absence of either medical or obstetric complications, 30 minutes or more of moderate exercise a day on most, if not all, days of the week is recommended for pregnant women."(1)  Such regular, moderate exercise is promoted for its overall health benefits for non-pregnant individuals(3), and pregnant women should be able to enjoy the same benefits.  Generally, exercise is safe and beneficial for both the mother and her baby.

Among other benefits, research indicates that "exercise may be beneficial in the primary prevention of gestational diabetes, particularly in morbidly obese women (BMI>33)."(1) This view has also been endorsed by the American Diabetes Association.(4)  In addition, exercise is likely to result in reduced lower back pain, better energy levels, improved stability and balance, faster recovery from labor, a possible shorter labor with less pain, and a faster return to pre-pregnancy weight, strength, and flexibility.  Exercise helps to prepare the body for the stresses of labor and delivery.(5,6,7)

 

GUIDELINES AND PRECAUTIONS FOR EXERCISE DURING PREGNANCY

A.  BASIS FOR GUIDELINES AND PRECAUTIONS

The guidelines and precautions to take while exercising during pregnancy are based on the adaptations that occur during pregnancy. These include cardiovascular, musculoskeletal, respiratory, and thermoregulatory changes that happen during pregnancy. In addition, the fetal responses to maternal exercise must be given priority in any recommendations. 

    1. Cardiovascular Adaptations.  During pregnancy, there is an increase in heart rate, blood volume, and overall cardiac output (the amount of blood pumped by the heart).(2)  By mid-pregnancy, cardiac output is up to 50% greater than before pregnancy. These cardiovascular changes appear to create a circulatory reserve necessary to provide nutrients and oxygen to both mother and fetus at rest and during moderate but not strenuous exercise.

There are several safety precautions that should be taken due to the cardiovascular adaptations that occur during pregnancy. After the first trimester, the supine position (lying on your back) results in relative obstruction of venous return and therefore decreased cardiac output. Therefore, after the first trimester, you should avoid exercising in the supine position. Heart rate monitoring devices may not work during exercise in pregnancy, so they should be used with caution if used at all.  In fact, even motionless standing also is associated with a significant decrease in cardiac output so this position should be avoided as much as possible.(8)

    2. Respiratory Adaptations.  For most pregnant women, more air is taken in and out with each breath.  This is referred to as an increased ventilation rate.  More oxygen is taken in, but it is used less efficiently.  However, for some fit women during pregnancy, there appear to be no changes in aerobic power or acid-base balance.

    3. Thermoregulatory Control.  During pregnancy, metabolic rate is increased, which results in increased heat production. Therefore, during exercise, there is an increased risk of overheating (hyperthermia), which could theoretically be dangerous to the fetus.  However, there have been no reports that hyperthermia associated with exercise is dangerous.

    4. Fetal Responses to Maternal Exercise.  There was a time in the past, when the maternal benefits of exercise were thought to be outweighed by the potential risks to the fetus. Now we have come to understand that there is very little risk in the uncomplicated pregnancy. The main unanswered question is does the redistribution of blood flow to the exercising muscles of the mother  interfere with the trans-placental transport of oxygen, carbon dioxide, and nutrients. If there are any effects, are they lasting? 

Most studies  that have measured fetal heart rate have found an increase of 10-30 beats/minute over baseline during and after maternal exercise. This increase has not been shown to have any lasting negative effects on the fetus.

There have been reports that have suggested a link between engaging in physical work or vigorous exercise and lower birth rate.  However, other reports have failed to find this association, which suggest that other factors, such as inefficient nutrition, are responsible for smaller fetuses.  According to the 2003 British Journal of Sports Medicine, "it appears that birth weight is not affected by exercise in women who have adequate energy intake." 

    5. Musculoskeletal Adaptations.  The most obvious change is the weight gain during pregnancy, which results in increased forces across the weight bearing joints, esp. the hips and knees. The fact that most of the weight occurs in the abdomen, which is more across the front of the body, it results in additional stress on the lower back.  An additional musculoskeletal change that occurs during pregnancy is increased ligamentous laxity results from the secretion of relaxin.  Relaxin is a hormone that causes the ligaments to relax, thus resulting in the the increased incidence of strains and sprains of the back, hips, and the other joints in the body.



B.  WARNING SIGNS AND CONTRAINDICATIONS

The 2002 ACOG guidelines include the following charts containing general guidelines about when not to exercise during pregnancy:

Warning signs to terminate exercise while pregnant(1)

* Vaginal bleeding
* Dyspnea before exertion
* Dizziness
* Headache
* Chest pain
* Muscle weakness
* Calf pain or swelling (need to rule out thrombophlebitis)
* Preterm labour
* Decreased fetal movement
* Amniotic fluid leakage

Absolute contraindications to aerobic exercise during pregnancy(1)

* Hemodynamically significant heart disease
* Restrictive lung disease
* Incompetent cervix/cerclage
* Multiple gestation at risk for premature labor
* Persistent second or third trimester bleeding
* Placenta previa after 26 weeks gestation
* Premature labor during the current pregnancy
* Ruptured membranes
* Pregnancy induced hypertension

Relative contraindications to aerobic exercise during pregnancy(1)

* Severe anemia
* Unevaluated maternal cardiac arrhythmia
* Chronic bronchitis
* Poorly controlled type I diabetes
* Extreme morbid obesity
* Extreme underweight (body mass index <12)
* History of extremely sedentary lifestyle
* Intrauterine growth restriction in current pregnancy
* Poorly controlled hypertension/pre-eclampsia
* Orthopedic limitations
* Poorly controlled seizure disorder
* Poorly controlled thyroid disease
* Heavy smoker

C.  GUIDELINES AND PRECAUTIONS FOR EXERCISE DURING PREGNANCY

There is no data that pregnant women should limit their exercise intensity or target heart rate because of potential adverse effects, unless they have medical conditions, such as poorly controlled diabetes. For women who do not have any additional risk factors for adverse maternal or perinatal outcome, the following recommendations may be made:

1.  Exercise during pregnancy, just like non-pregnant exercise, should include activities to improve cardiovascular fitness (aerobic exercise), to improve strength (resistance training), and to improve flexibility (stretching).

2.  Aerobic exercise can consist of any continuous, rhythmic activities that use large muscle groups, such as walking, hiking, running, aerobic dance, swimming, cycling, rowing, cross country skiing, etc... Activities that increase the risk of falls, such as skiing, horseback riding, and skating, probably should be avoided. Non-jarring exercise, such as walking, swimming, and stationary cycling, is to be preferred over jarring exercise, such as jogging and tennis.  

3.  Regular exercise (at least 30 minutes at least 3 times per week) is preferable to intermittent activity. Pregnant women who have been sedentary before pregnancy should follow a gradual progression of up to 30 minutes a day.

4.  Women should avoid exercise in the supine position after the first trimester. Such a position is associated with decreased cardiac output in most pregnant women due to the fetus pressing on the vena cava. Because the remaining cardiac output will be preferentially distributed away from the uterus during vigorous exercise, such exercise is best avoided during pregnancy.

5.   Weightlifting should be limited to light to moderate weights.  Holding the breathe and isometrics should be avoided.

6.    Avoid overstretching the joints, as ligaments are looser due to secretion of relaxin, which helps the body prepare for the birthing process.  

7.   Pregnant women who exercise in the first trimester should augment heat dissipation by ensuring adequate hydration, appropriate clothing, and optimal environmental surroundings during exercise. This means drinking plenty of water before, during, and after exercise.

8.   Scuba diving should be avoided during pregnancy because the fetus is at increased risk of decompression sickness.

9.   Abdominal exercises should be continued throughout pregnancy, as they can help make pushing the baby out easier as well as help with low back pain. However, they should not be performed on the back after the first trimester.

10.  Maintain proper posture while exercising, whether sitting or standing.

11.  Eat a small meal before exercise and drink plenty of water before, during and after exercise.  

REFERENCES:
1. ACOG Committee. Opinion no. 267: exercise during pregnancy and the postpartum period. Obstet Gynecol 2002;99:171–3.
2. Artal R, O'Toole M. Guidelines of the American College of Obstetricians and Gynecologists for exercise during pregnancy and the postpartum period.  Br J Sports Med 2003;37:6-12
3. American College of Sports Medicine: Guidelines for exercise testing and prescription. 6th edition. Philadelphia: Lippincott, Williams, and Wilkins, 2000.
4. Jovanovic-Peterson L, Peterson CM. Exercise and the nutritional management of diabetes during pregnancy. Obstet Gynecol Clin North Am 1996; 23: 75-86.
5. Hall D, Kaufmann D. Effects of Aerobic Strength Conditioning on Pregnancy Outcomes. American Journal of Obstetrics and Gynecology. 1987; 157: 1199-203.
6.  American Journal of Public Health. 1998; 88:1528-1533.
7.  Bryant CX, Peterson JA, Graves JE. Muscular strength and endurance. ACSM's Resource Manual for Guidelines for Exercise Testing and Prescription--4th ed. Philadelphia, PA: Williams & Wilkins. 2001. 460-467.
8.  Clark SL, Cotton DV, Pivarnik JM, et al., Position change and central hemodynamic profile during normal trimester pregnancy and post-partum. Am J Obstet Gynecol 1991; 164:883-887.