How Pregnancy Changes Your Body

A Healthful Mission

BeFit-Mom's mission is to help all women stay fit and healthy during pregnancy and beyond. Science now acknowledges these goals as not only medically sound, but beneficial for both the mother-to-be and her developing baby. Data from clinical studies has shown that fit moms have better control over weight gain, easier labor, leaner, healthier babies and they bounce back faster from pregnancy and childbirth than do sedentary women. A full discussion of the value of exercise during pregnancy can be found on the Benefits of Exercise During Pregnancy page of this web site.

Knowledge Is Your Ally

Your body will undergo tremendous changes during your pregnancy and postpartum periods, changes that may at times cause concern. Leading obstetrician and pediatrician Dr. Barry Brazelton stresses that because the mother's mental state influences the health of her baby, it is crucial for her to a maintain calm, positive state of mind during pregnancy. Knowing with reasonable certainty how to manage these changes-while safely engaging in activities that enhance the health of you and your baby-can give you invaluable peace of mind.

Bodily Systems Impacted during Pregnancy

During pregnancy, your body produces special hormones that stimulate physical changes in virtually every part of your body. Knowledge about these biomechanical changes in your
Metabolism Cardiovascular exercise  and Musculoskeletal  systems is your best ally in your mission to have the healthiest pregnancy possible.

The Cardiovascular System

During pregnancy, the woman's cardiovascular system expands to support the needs of the growing Fetus . These changes include:

  • Boosts your Blood volume , the amount of blood circulating through your body, by 40% to 50%.
  • Raises your resting heart rate by about 15 to 20 beats per minute (BPM) by the third trimester.
  • Elevates Cardiac output , or amount of blood pumped per minute.
  • Increases Stroke volume, the amount of oxygenated blood pumped in one heartbeat.
  • Expands Tidal volume , or the amount of air you take in per breath.
  • Dilates and relaxes your blood vessels, thereby decreasing resting blood pressure, and aiding in circulation.


What Pregnancy Does to Your metabolism

  • Boosts Basal metabolism .
  • Raises your core temperature slightly.
  • Slightly elevates your insulin levels.
  • Elevates your daily caloric needs by 300 calories by second trimester.
  • Increases your protein and fluid requirements.

How Posture and Spine Alignment Change during Pregnancy

Illustration of Pregnancy Posture: IdealIllustration of Pregnancy Posture: Tipped Pelvis


Though subtle, the postural changes of pregnancy have profound effects on many areas of your body. As the weight of your baby grows and the Uterus expands, the pelvis tips to counterbalance the load. The pubic bone and tailbone move backward, thereby increasing the arch in your lower back. In fitness terminology, this is called an Anterior  tilt of the pelvis or a Lordotic  posture.

Because the spine is a dynamic structure, alignment changes in the pelvis have a ripple effect on the rest of the spine. TheThorax, or upper back, increases its curve, which rounds the shoulders forward and collapses the chest. In response to the increased thoracic curve, the head to slides forward. Too much curve in the upper back Vertebrae is referred to as a Kyphotic posture. So during pregnancy, women experience a compound alignment problem; a Kyphotic /Lordotic  posture, which augments all of the natural "S" curves of the spine.

These postural misalignments have a series of adverse effects including:

  • Compression the vertebral discs
  • Increased strain on the Articular  surfaces of the spine
  • Reduction of lung capacity
  • Loss of height
  • Ligament  strain
  • System wide changes throughout your muscular system

As pregnancy advances, the ribcage also expands dramatically, providing needed additional space for the lungs as the Uterus expands and fills the abdominal cavity.

Muscular Imbalances of Pregnancy

To compensate for these postural deviations, specific muscle groups must work harder to support the body in the upright position. Over time, these muscles shorten and become Hypertonic , or chronically too tight. Opposing muscle groups need to work less to support the body, and weaken and atrophy, or become Hypotonic . These postural and muscular changes tend to be self-reinforcing. As the belly expands, the postural deviations worsen, which in turn, further augment muscular imbalances.

However, you can prevent or lessen most of these conditions with a prenatal exercise program that focuses on counterbalancing these effects by:

  • Stretching muscle groups that tend to over-tighten
  • Strengthening muscle groups that tend to weaken
  • Choosing core strength and stability exercises that incorporate the Neutral spine position

Muscles that Tighten during Pregnancy

Muscles that Weaken or are Over-Stretched during Pregnancy

  • Buttocks; Gluteals  or hip extensors
  • Hamstring muscles; back of the thigh
  • Abdominal muscles*
  • Mid and lower fibers of the Trapezius in the upper back
  • The external rotators of the shoulder
  • Serratus Anterior ; Scapular depression:
  • Neck flexors, frontal only
  • Pelvic floor  muscles
  • Intercostals; ribcage muscles

* For more information on how pregnancy impacts the abdominal wall, see the Abdominal Reconditioning After Pregnancy and Diastasis Recti page of this web site.

Pregnancy's Impact on Connective Tissues and ligaments

Pregnancy hormones stimulate lengthening and Laxity  in the ligaments and other connective tissues, which allows the Pelvic outlet  to expand during labor and delivery. Ligament  Laxity  leaves joints more vulnerable to injury and the postural effects of:

This discussion has provided an overview of the physiological adaptations of pregnancy. We encourage you to consult other sections of this web site for further details on how to protect your body, and how to optimize your physical fitness during and after pregnancy.

Here at BeFit-Mom, you'll find a wealth of free, in depth, expert information and advice about prenatal and postpartum fitness and exercise to help you have the healthiest pregnancy, and the healthiest baby.

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Our mission is to educate, motivate, and support prenatal and postnatal women, and to inspire women to lead their entire families to better health and wellness.