Exercise and Pregnancy
Exercise and pregnancy? I'm
approached regularly by patients who are pregnant or trying to become
pregnant, but are concerned that they'll have to curtail their gym or
exercise program as they get larger. They ask me "Will exercises harm
the baby?", "Can exercise possibly induce premature labor?", "Could I
injury myself", "Which exercises should I do?" Every woman and every
pregnancy is completely different.
It is therefore critical that you consult your obstetrician before
embarking on an exercise program.
Exercise and pregnancy can coexist.
Studies have shown that exercising,
besides giving the benefits of maintaining fitness, can also attenuate
the symptoms of nausea, fatigue, and back pain. The American College of
Obstetrics and Gynecology is now emphasizing the importance of exercise
before, during and after pregnancy. Years ago doctors restricted the
type of exercise that was safe; today the emphasis is on promoting
pregnancy so long as certain precautions are followed.
The exercise you do on the exercise
ball can gently work the muscles that help support your back during
pregnancy. Also advertised as the "birthing ball", the exercise ball is
helpful for easing labor and delivery. Once the baby is born, you can
get back into exercising easily using the ball again. The rationale of
exercise and pregnancy includes relief of low back pain, preparation
for labor and delivery by increasing strength, endurance, and tolerance
for the physical and mental stress. Posture may be improved and
postpartum recovery may be easier and faster.
postnatal women must get clearance from their physicians before
participating in an exercise program. They must be screened
for conditions that would limit their medical, cardiovascular,
musculoskeletal, or pregnancy related complications.
American College of Obstetricians and Gynecologists
has the following recommendations regarding exercise and pregnancy -
discontinuing exercise under the following circumstances:
are best to consult their physician for advice regarding exercise
and pregnancy if they have conditions such as
factors for preterm labour
rupture of membranes
experts suggest that you adhere to the guidelines suggested by the
or respiratory condition
history of premature labor
3 to 5 times per week
Maximum of 40 minutes per session
Low impact aerobic type exercise
Months 1 to 3
If you are were active several months prior to the pregnancy you should
remain active but adhere to the FITT guidelines. If you were inactive
prior to your pregnancy, hold off exercising for the first three
months. Your usual routine is safe. Listen to your body.
Nausea and fatigue may limit your endurance so shorten your routine,
reduce its frequency, or change the time of day you exercise. During
this period it is still safe to lie on your back. Take this opportunity
to strengthen your abdominal musculature as this will weaken very
quickly once your abdomen starts to expand. Women with strong abdominal
muscles will return to their pre-pregnant figures faster after giving
birth, and will suffer less back pain.
Months 4 to 9
Previously active women are able to increase their exercise intensity
during the second trimester by 10-15% but within the target zone
established by your health care professional. Previously inactive women
may begin low impact aerobic activity such as walking, swimming, or
Changes occur in your body during pregnancy that can affect your
ability to exercise while pregnant:
The hormones produced during pregnancy, especially the last trimester,
cause the ligaments that support your joints to become more elastic.
This causes your joints to lose stability and are therefore at risk for
injury. You should avoid sudden bouncing, jerking, or high impact
activities. Be careful when exercising if you notice loose or unstable
As you gain weight, your centre of gravity changes and therefore your
posture changes, putting strain on new muscles and ligaments. This can
result in altered balance and increased risk of falls. Most exercise
ball exercises require some degree of balance so be aware of this and
adapt your movements accordingly.
Your heart needs to work harder at rest due to the increase in weight,
and therefore works even harder when your muscles are demanding
increased oxygen. Increases of up to 50% in cardiac output, 15 beats
per minute in resting heart rate, and 45% increase in blood volume can
occur by the third trimester. The body may divert blood flow from some
parts of your body
in order to meet the needs of the muscles. It is therefore important
not to overdo it. Standing for long periods can reduce placental blood
flow so keep changing positions.
Both pregnancy and exercise increase your metabolic rate and therefore
core body temperature. It is also know that core temperatures in excess
of 102.60F are potentially teratogenic in the first three months. While
adaptive changes that occur to the woman's body during pregnancy help
dissipate this extra heat, it is still prudent to maintain adequate
hydration and avoid exercising in hot or humid environments. To avoid
compromising fetal growth, caloric intake should be adequate to offset
the combined needs of pregnancy and exercise (typically an extra 300
calories a day).
Pregnancy and exercise both increase the bodies need for oxygen. Oxygen
requirements during pregnancy are greater therefore limiting your
ability to perform high intensity activities. You need to heed signs of
fatigue and stop workouts short of exhaustion to reduce the potential
risk of hypoglycemia. Sessions for recreational athletes are best
limited to 45 minutes.
Increasing abdominal size: The weight of the growing fetus will
compress the inferior vena cava and hence affect blood return to the
heart possibly causing your blood pressure to drop when lying in the
supine position. This can disrupt the oxygen supply to the fetus.It is
obvious then to avoid the exercise ball exercises that require you to
be in the supine position. Prone abdominal hollowing, and
pelvic tilts in standing can be used to activate the abdominal muscles.
The increase in abdominal size puts extra strain on
the supporting back muscles so avoid those more
advanced exercises such as
hopping or skipping
Supportive bras and back braces are now available to assist you with
these changes as you exercise. Exercise and pregnancy can go hand in
Physiology of Exercise and
multiple organ systems are involved in creating the optimal environment
for the fetus, the physiology of gestation is complex. The impact of
exercise and pregnancy and its physiologic variables has been studied,
but there is no agreement about some aspects of cardiopulmonary and
metabolic response. Studies involving human subjects have
inconsistent, partly because of differences in study design, exercise
regimens, and the fitness level of the participants. Prospective,
adequately controlled studies of humans are few, so animal models have
been used to elucidate the interaction of exercise and pregnancy.
energy cost of pregnancy is higher than that of the non pregnant state
by an average of 300 k.calories per day, exercise also increases
caloric expenditure. So pregnant women who exercise need to consume
enough calories to meet these increased needs. Physically active
pregnant women should eat enough to satisfy their appetite, preferable
a diet rich in complex carbohydrates. Weight should be monitored to be
sure that gains are steady and adequate.
Hyperthermia during pregnancy is a potential teratogenic risk to the
fetus. Some experts are concerned that pregnant women who exercise may
increase their body temperatures to dangerous levels. However, studies
show that exercise does not cause the same level of increase in body
temperature in pregnant women as it does in non-pregnant women. This
may be because the work intensity achieved by pregnant women is not
high enough to
cause such a rise. Pregnant women also may be better able to cool
themselves with changes in regional blood flow.
to mix exercise and pregnancy must drink adequate fluids. They should
drink up to a pint of liquid before exercising, and a cup of liquid
every 20 minutes during exercise. Even if they are not thirsty after
exercise, they should drink enough to replenish lost fluids( 1-2 litres
of fluids per hour may be lost through sweating)
also should be cautioned against exercising when the weather is hot
and/or humid, or when they have a fever. In general, the higher the air
temperature, the lower the humidity, the concern with exercise and
pregnancy must be to avoid heat injury. For
example, if the air temperature is above 80 degrees Fahrenheit,
humidity should be no higher than 50%. Also, it's safer to exercise
before 8 am and after 6 pm.
The weight of the growing fetus increases lumbar lordosis, moving the
centre of gravity to the pelvis and causing a
compensatory increase in cervical spine flexion. Balance may become
precarious as movements are modified to accommodate these changes.
Pregnant women should be told that exercises involving sudden changes
in body position carry a greater risk of falls. Sports with the
potential for abdominal trauma, such as surfing, horseback riding, or
trampoline exercise, should be avoided.
Ligaments relax as connective tissue softens in response to hormone
changes early in pregnancy. This increased joint mobility may
facilitate delivery of the baby, but it
also may make women more vulnerable to sports induced injury during
exercise and pregnancy. Softening of connective tissue and
increased lordosis is also related
to the back pain that often occurs in pregnancy.
warm up is important to avoid sprains. Pregnant women who do resistance
exercise should use light weights so that joints are not excessively
Water retention in the third trimester may reduce mobility
at the wrists and ankles and lead to carpal tunnel syndrome, causing
sensory changes and muscle weakness. Activities involving strength and
agility of the hands such as tennis and skiing may make pregnant women
more injury prone during exercise and pregnancy.
Cardiac output increases by 30-50% during pregnancy, peaking in the
second trimester. It is variable in the third
trimester but decreases when the woman is in the seated or supine
position because of decreased venous return. Both components of cardiac
output -heart rate and stroke volume - increase. The stroke volume is
greatly affected by an increase in heart size, with left ventricular
volume enlarging considerably by term. The responses to exercise of
both stroke volume and cardiac output are significantly increased
during pregnancy. An increase in blood volume parallels the increase in
cardiac output to some degree. The volume of plasma component of blood
increases up to 50%, but red cell volume increases only up to 20%,
resulting in the relative anemia of pregnancy, with hematocrit dropping
from a normal of 40% to about 35%. This is similar to the pseudo anemia
seen in endurance athletes and may be more significant in pregnant
endurance athletes. Oxygen distribution to tissues is not affected by
this drop in hematocrit as seen by the decreased arteriovenous oxygen
The resting heart rate rises in the first weeks of
pregnancy by about 7 beats per minute and plateaus after 32 weeks at a
rate approximately 16 beats per minute faster than the prepregnancy
rate. Studies of fetal growth and development show that increases or
decreases in fetal heart rate during exercise are transient and produce
no deleterious effects.
The mean arterial blood pressure of a pregnant woman drops reaching its
lowest value at mid pregnancy and returning to near prepregnancy levels
at term. Systolic blood pressure changes very little, so women have an
increased pulse pressure and
throbbing pulse. Peripheral resistance also decreases, allowing an
increased cardiac output with a drop in blood pressure.
output and blood pressure may vary with changes in body position. When
a pregnant woman is in the spine position, the uterus rests on the
vertebral column and can compress the inferior vena cava and abdominal
aorta, causing a drop in cardiac output and resultant hypotension.
The decreased venous return raises the concern of whether certain
positions assumed during exercise compromise blood flow to the fetus.
Exercises performed when a woman in in the supine position are not
recommended after the first trimester. Motionless standing can cause an
even greater drop in cardiac output and should be avoided when
Blood to skeletal muscles and the fetus is in parallel circulation, and
a potential problem is that blood may be shunted toward exercising
muscles and away from the fetus. Animal studies show that although
uterine blood flow transiently decreases during exercise and pregnancy,
uterine oxygen extraction increases markedly during pregnancy, and
fetal and placental oxygen levels are maintained.
during exercise occurs to a greater degree in pregnancy than in the
nonpregnant state, enhancing oxygen delivery.
oxygen consumption increases during pregnancy by about 40 ml/min, with
the fetus, placenta, heart, and kidneys consuming the most oxygen.
Pregnant women increase ventilation by breathing more deeply rather
than more frequently. Although the diaphragm rises with the increasing
size of the uterus, the total lung capacity and vital capacity change
very little. Tidal volume increases up to 40% as the woman
breathes more deeply, and residual volume and expiratory reserve volume
become smaller to compensate. This results in a smaller oxygen reserve
in the lungs at the end of a quiet expiration, and less ability to
withstand apnea. For this reason, scuba diving and sprinting are not
recommended during pregnancy.
Pregnant women respond differently to
physical exercise than do nonpregnant women. They also show greater
variability in response to the physiologic challenge of exercise. The
increase in body weight and reduced efficiency of oxygen utilization
requires a greater oxygen cost for any given weight bearing exercise.
The reasons for this greater oxygen cost are not entirely understood.
Some studies indicate that women who exercise during pregnancy may have
a training effect, increasing their aerobic capacity.
Many women experience a decline in exercise performance during
pregnancy and are unable to maintain high levels of aerobic exercise.
This decrease in exercise tolerance is due in part to a lower
cardiopulmonary reserve, but factors such as fatigue, nausea and
vomiting and changes in body configuration may also contribute. There
is some indication that non weight-bearing exercises such as swimming
and cycling are better tolerated by pregnant women.
Exercise during pregnancy maintains
muscle tone, strength, and endurance and it may protect against back
pain and other discomforts. Subjective benefits such as improved mood,
energy level and self-image have been reported. Women who exercise
regularly at a moderate intensity can maintain cardiorespiratory
fitness during pregnancy and reduce the risk of postpartum obesity.
Most evidence suggests that moderate exercise during normal pregnancy
has no adverse or beneficial effects on maternal weight gain, length of
gestation, length of labour, infant birth weight or APGAR scores. One
must be wary when exercising while pregnant because there are flaws in
the studies available about the effects of exercise on pregnancy and a
lack of studies using human subjects.
All pregnant women need a medical and obstetric examination before they
begin an exercise program.
Contraindications to exercise and pregnancy should be ruled out, and
conditions such as chronic hypertension or active thyroid, cardiac,
vascular or pulmonary disease need a careful evaluation to determine if
they are candidates for regular exercise.
Useful Links for
information on Exercise during Pregnancy
the American College of Obstetricians and Gynecologists' Educational
Brochure on exercise and pregnancy click on the following link:
Guidelines of the American College of Obstetricians and Gynecologists
for exercise and pregnancy and the postpartum period click on the
Exercise ball is
sometimes referred to as the birth ball or birthing ball. For more
information on the birth ball click on the following link:
sport specific guidelines
for exercise and pregnancy click on the following link:
Sport Specific Guidelines for Exercise during Pregnancy