Exercise in Pregnancy

Is it safe?

American College of Obstetrics and Gynecology, 2002: Moderate exercise (30 mins or more daily) on most if not all days of the week recommended for women with low risk pregnancies.

Society of Obstetricians and Gynecologist of Canada / Canadian Society for Exercise Physiology, 2003: All women without contraindications should be encouraged to participate in aerobic and strength-conditioning exercises.

Maternal Benefits:

• Strengthen muscles that are stressed by pregnancy - less back pain
• Possibly an easier labor
• Improved sense of well being
• Increased energy
• Improved sleep
• Less anxiety
• Possibly less weight gain
• Less symptoms of pregnancy (nausea, heartburn, leg cramps, round ligament pain)

Risks of NOT exercising during pregnancy include increased risk of:

• Loss of muscular and cardiovascular fitness
• Excessive maternal weight gain
• Gestational diabetes
• Pregnancy-induced hypertension
• Development of varicose veins
• Deep vein thrombosis

Exercise and Gestational Diabetes

Artal study: Similar maternal and fetal outcomes for patients treated by exercise and diet versus insulin and diet.

Physical activity during the year before pregnancy significantly reduced risk of gestational diabetes compared with inactive women (OR 0.45). This protective effect is seen especially in women with a body mass index greater than 25.

Exercise and Preeclampsia

Women who exercise regularly before and during pregnancy may have reduced risk (OR 0.65), however the evidence supporting this is weaker than for the effect of exercise on development of gestational diabetes.

Does exercise influence the rate of epidurals, cesarean sections and assisted delivery?

Clapp,1990: prospective observational study of 131 women found that in women who exercise during pregnancy, there were fewer epidurals, more vaginal deliveries, fewer assisted deliveries and cesarean sections, and shorter active phase of labor.

Magann et al, 2002: prospective observational study of 750 military women found more inductions, longer first stage of labor and no difference in mode of delivery, 2nd or 3rd stage of labor, or epidural use.

Why different delivery outcomes?

This may be due to variables such as different pre-pregnancy fitness levels, different intensity, type and duration of exercise, and different control groups used in each study. Bottom line: No clear effect of maternal exercise on the mode of delivery.

Exercise and Preterm Labor

No strong evidence from studies showing an increase in preterm labor. One study showed no difference in preterm labor, however a slightly shorter gestational length (average of 5 days).

Other Maternal Health Benefits

• Increased HDL "good cholesterol" and decreased triglycerides
• Decreased blood pressure
• Decreased coronary artery disease
• Increased longevity

Maternal Physiology and Exercise

Cardiovascular: Increase in blood volume, plasma volume, and red blood cell mass in pregnancy. Blood volume increases an additional 20% in women who continue to exercise. There is an additional 40% increase in cardiac output if a woman continues to exercise in pregnancy.

Uterine blood flow: Reduced blood flow to uterus, however smaller effect if well conditioned

Compensation mechanisms include a preferential flow to the placenta and away from uterine muscles, as well as increased oxygen extraction by the fetus/placenta.

Temperature Effects

Studies show an increase in neural tube defects such as spina bifida from maternal fever or hot tub exposure. However, there are no reports in humans that elevated core body temperature associated with exercise causes malformation. Animal/human studies show that changes in core temperature are related to the intensity and duration of exertion. One study found that moderate intensity exercise up to 30 minutes raised core body temperature no more than 38C (100.4F).

Protective effects against elevated temperatures in pregnancy include improved heat dissipation due to the increase blood volume. The increase in maternal mass means that more heat must be generated to raise the core body temperature the same amount. Also, the temperature at which sweating begins falls.

Fetal Outcomes

No increase in early pregnancy loss.
Birth weight: inconsistent results but in general the effect of exercise on fetal weight is considered safe. This is related to re-pregnancy maternal fitness, the trimester in which the exercise is performed and the intensity of exercise. In one study, infants were up to about one pound less in women who exercised more intensely and into the third trimester.

Fetal Heart Rate Patterns

Study: Carpenter et al found no difference in the mean fetal heart rate; all babies had reassuring tests 30 minutes after exercise. Other studies showed a mild transient increase in fetal heart rate.

The increase in fetal heart rate baseline is thought to be due to a more awakened fetal state, maternal catecholamines passing to the fetus, and increase in core temperature.

No negative impact on 1 or 5 minute Apgar scores. Two studies showed a significant decrease in umbilical cord abnormalities (nuchal cord and true knot). Children do not appear to suffer any adverse neuro-developmental outcomes or growth problems at 1 and 5 years.

Absolute Contraindications

• Restrictive lung disease
• Incompetent cervix/cerclage
• Multiple gestation at risk for premature labor
• Persistent second- or third-trimester bleeding
• Placenta previa after 26 weeks of gestation
• Premature labor during the current pregnancy
• Ruptured membranes
• Preeclampsia/pregnancy-induced hypertension

Relative Contraindications

• Severe anemia
• Unevaluated maternal cardiac arrhythmia
• Chronic bronchitis
• Poorly controlled type 1 diabetes
• Extreme morbid obesity
• Extreme underweight (BMI < 12)
• History of extremely sedentary lifestyle
• Intrauterine growth restriction in current pregnancy
• Poorly controlled hypertension
• Orthopedic limitations
• Poorly controlled seizure disorder
• Poorly controlled hyperthyroidism
• Heavy smoker

Warning Signs

• Vaginal bleeding
• Dizziness/lightheadedness
• Worsening shortness of breath
• Chest pain
• Headache
• Calf pain or swelling
• Uterine contractions
• Decreased fetal movement
• Fluid leakage from the vagina

General Guidelines

• After the first trimester avoid doing exercises on your back
• Avoid intense exercise in hot, humid weather or when you have a fever
• Drink plenty of water to prevent overheating and dehydration
• Healthy diet

Safe Exercises

• Walking
• Swimming
• Stationary or recumbent cycling
• Aerobics: low impact and water
• Moderate running

How intense?

"Talk test:" if you can carry on a conversation, then the intensity is appropriate.

Modified Heart Rate Target Zones from the Canadian Society of Exercise Physiology:

Avoid sports that increase risk of injury or falling:

• Racquet sports
• Downhill snow skiing
• Contact sports
• Also avoid scuba diving*

*Scuba diving should be avoided throughout pregnancy because during this activity the fetus is at increased risk for decompression sickness secondary to the inability of the fetal pulmonary circulation to filter bubble formation.