Effects of Pregnancy on Your Body

Aside from simply the changes in body image, there are many other changes a woman's body undergoes during pregnancy. The extent of these changes varies from person to person, and is dependent on things such as gestational age, pre-pregnancy fitness levels, and body composition. Some of the major physiological and anatomical changes the body undergoes are reported below.

As pregnancy progresses and the size of the uterus increases, the heart is displaced upward and slightly to the left within the chest cavity. The wall of the heart thickens as the muscle works harder to support the pregnancy (4).

The heart adapts to increased demands on it by the enlarging uterus, and growing fetus by increasing Cardiac Output (amount of blood pumped by the heart in one minute) rises 30-50% during pregnancy (1). Cardiac output increases during pregnancy because there is a decrease in the resistance to blood flow as more blood flows to the placenta. Gestational hormones also cause blood vessels to relax, which both allow blood to flow through the body easier and faster, so more blood can be pumped more often (5). Blood volume also increases, rising 35% to 45% over the pre-pregnant state. To offset the increased volume so that blood pressure isn't increased the circulatory system adapts by increasing the capacity of the veins. Greater vasodilation is another circulatory adaptation that occurs during pregnancy to increase heat loss and reduce the tendency for hyperthermia (2).

There is a greater increase in blood plasma than red cell mass, therefore anemia (insufficient number of red blood cells) often occurs during pregnancy (1). Endurance athletes may notice an improvement in their performance early in pregnancy as their blood volume and red blood cell mass will have increased, before an increase in body weight and uterine size begins to occur. This could cause changes similar to a blood-doping effect, where there is an increase in the oxygen-carrying capacity of the blood in the athlete (1).

As the uterus enlarges, rising higher and higher in the abdomen, it prevents the diaphragm from being drawn down completely during respiration. The diaphragm is a dome-shaped sheath of muscle that separates the thoracic and abdominal cavities. This can make deep breathing uncomfortable and difficult (4). Respiration rate is found to increase during pregnancy, which means the body is having to work harder to provide enough oxygen to the developing fetus (3). The aerobic capacity (individuals ability to perform work) depends on oxygen consumption and utilization, otherwise known as VO₂max (4). Cardiovascular training has been claimed to improve VO₂ max by up to 33%; however, studies haven't been able to prove that this increase isn't due to the increased oxygen carrying capacity of Hemoglobin that occurs as a result of the rise in blood volume (4).

Relaxin is a hormone produced during pregnancy that causes joint laxity. It allows softening of the supporting ligaments in the body's joints, and the connective tissues in the pelvic girdle to relax and soften. This results in increased flexibility which is needed to widen the pelvis so that the baby can pass through the birth canal (4). This can make pregnant women more prone to muscle and soft tissue injuries. The increased looseness of the sacral bone at the back of the pelvis can lead to considerable discomfort in the lower back (4).

Weight gain increases average 1 to 3 kg in the first trimester, 6 to 8 kg in the second trimester, 3.5 to 4 kg in the third trimester, and tends to plateau near term. The total weight gain during pregnancy averages about 12 kg, and the distribution of this weight is shown in the table below (5).

Contributing Factor	Weight Gain
Infant at Birth	3.5 kilograms
Placenta	0.7 kilograms
Amniotic Fluid	0.8 kilograms
Maternal Blood Volume and Extracellular Fluid	2.0 kilograms
Maternal Fat Stores	2.5 kilograms
Uterus	1.0 kilograms
Breasts	1.5 kilograms
Total	12.0 kilograms

As the baby grows the abdominal organs are pushed up and the center of gravity shifts forward, causing shifts in the mothers center of gravity. The body compensates for this forward shift in the center of gravity by increasing the amount of curvature in their spine (Lordosis) and a forward tilt of the pelvis (3). Increased breast mass is also compensated for by adjusting the posture of the head, and the amount of curvature in the spine. The instability of the pelvis (a result of Relaxin secretion), and the unstable posture created by the increase in body weight, result in a wide-based form of walking called "waddling gait" (3). These changes in posture make it difficult for some women to continue participating in competitive sport, as well as increase the risk of falling and losing balance.

The overall prevalence of back pain during the 9-month period is thought to be approximately 50%. Pain can begin before the 12th week and continue up to 6 months postpartum (3).

Various studies found that the risk factors that contributed to back pain during pregnancy were pre-pregnancy back pain and multiparity (giving birth to twins, triplets, etc.), whereas age, height, weight, race, fetal weight, and socioeconomic status do not seem to correlate (3).

At conception the body begins to release increased amounts of hormones that soften ligaments and fibrous tissues and loosen the joints. This allows the body to make room for the expanding uterus, but it also predisposes the body to more stress and strain than before conception.

The back and abdominal muscles support the spine and keep it in proper alignment. In response to the growing fetus, the abdominal muscles often separate because of the amount of stretching they need to undergo. This condition is termed Diastasis Recti. This condition causes the back muscles to compensate for the abdominal muscles in holding the spine erect- causes tight, stressed muscles. Even if Diastasis recti does not occur, the abdominal muscles lose their tone and become less effective at helping to maintain a neutral posture.

Initial treatment for pregnant patients with back pain consists of such things as heat and ice. Massage therapy may also provide short-term pain relief. Proper neutral posture can be taught by a physician as well. Pregnant Women should be taught to perform all activities in the neutral spine posture; observing the patient in a physical therapy office simulating her usual daily activities can ensure that she knows how to maintain a neutral spine.

Exercise programs are often used to improve the strength and condition of supporting structures. The exercise helps the patient maintain a neutral spine posture, promote biomechanic efficiency, and minimize stress on the back.

NOTE - Physically fit women who get 45 minutes or more of physical activity a week are less likely to develop back pain during pregnancy (3).

1. Araujo, D. (1997) Expecting questions about exercise and pregnancy. The Physician and Sportsmedicine, 25 (4).

2. Artal, R. (1999) Exercise During Pregnancy: Safe and Beneficial for Most. The Physician and

3. Colliton, J. (1996). Back Pain and Pregnancy: Active Management Strategies. The Physician and Sportsmedicine, 24 (7).

4. Freyder, S. Connelly. (1989). Exercising While Pregnant. JOSPT, March, 358-364.

6. Wolfe, Larry A. (1993). Pregnancy. In J. Skinner, Exercise Testing and Exercise Prescription for Special