The Basics: Physiological changes in Pregnancy

The Basics: Physiological changes in Pregnancy

28 June 2017

The evidence in favor of exercise during pregnancy is so strong that the American College of Obstetricians and Gynecologists (ACOG) encourages pregnant women to do moderate exercise for 30 minutes or more every single day.

Studies have even shown that very physically active women can benefit from continuing their high volume exercise routines, as much as 9 hours per week, into pregnancy.


During pregnancy, the pregnant mother undergoes significant anatomical and physiological changes in order to nurture and accommodate the developing foetus. These changes begin after conception and affect every organ system in the body.

In order to understand what you or your client should and shouldn’t due during pregnancy, you need to understand what these changes  are and how to programme a safe exercise regime based on them.



The respiratory rate rises to compensate for increased maternal oxygen consumption, which is needed for the demands of the uterus, placenta and fetus. There is decreased functional capacity, increased tidal volume and respiratory alkalosis and of course when you preggos, you always feel out of breathe.


Blood volume increases dramatically, more blood vessels grow and the pressure of the expanding uterus on large veins causes the blood to slow in its return to the heart. .Her resting heart rate will be elevated and in the second trimester she will experience decreased blood pressure.

Endocrine System:

The placenta is now producing large amounts of estrogen and progesterone. She may feel a lot warmer or experience “hot flushes” due to the increase in hormones and basal metabolic rate.

Urinary system:

The uterus will put pressure on the bladder, urethra and pelvic floor muscles which leads to temporary bladder problems like frequent urination and even leaking when coughing, sneezing and laughing. The kidneys are also under a lot more load to excrete the mother's and fetus waster products.

Musculoskeletal System:

There is a realignment of the spine to maintain balance which results in a shift in posture. Relaxin increases ligament laxity which can contribute to back pain and pubic symphysis dysfunction. The ligaments that hold the pelvic bones together loosen to prepare for birth. The abdomen expands and the abdominal wall and ligaments that support the uterus will stretch.

What does the above mean in terms of exercise?

The general rule of thumb is:

  • Use the “talk test” or ratings of perceived exertion (RPE) as a  monitor of exercise intensity.
  • Be aware that the cardiovascular and hormonal changes cause some of the early pregnancy symptoms of fatigue, shortness of breath, nausea, light-headedness, and dizziness when getting up so bear that in mind when working out.
  • Be wary of overheating and make sure you drink a lot of water. Pregnant clients will probably notice that they feel warmer and the skin flushes more easily.
  • After the first trimester, it is advised to stay off your back as pressure from the growing fetus would rest on the vena cava leading to a reduced return of blood flow to the heart.
  • The pressure on the pelvic floor may result in leakage - refrain from adding more pressure by eliminating high impact movements such as jumping.
  • The separation of the abdominals can be further exacerbated by continuing to do core exercises.

Research continues to identify the many positive benefits of exercise during pregnancy for both the mother and baby, but there are contraindications to exercise and signs to stop exercising that fitness professionals should know and follow (Table 1.1).

Pregnant clients should also obtain medical clearance for participating in an exercise program and be monitored throughout their pregnancy.

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