Pregnancy: Understanding Changes To An Expectant Woman’s Body

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Extensive physical and physiological changes take place in an expectant woman. This happens through the actions of the hormones, oestrogen, progesterone and relaxin. These changes create challenges, which should never be undermined. Hence it is important to understand the effects on the woman’s body during pregnancy to learn to cope with the challenges.

Respiratory System

There is an increased demand for oxygen. This is because the basal metabolic rate and the mass of the expectant woman will increase as well. A woman will require about 20% more oxygen than normal at term. She will also exhales more carbon dioxide which triggers the already sensitive respiratory system to increase the respiratory rate slightly. Hence, it is this lowering of the carbon dioxide that leads to pregnant women to become breathless on activity.

In addition, many expectant women will experience the ascending uterus. The descent of the diaphragm, needed for deep breathing, is progressively obstructed. It can force the diaphragm upwards by at least 4cm towards the end of pregnancy. Hence, this rising pressure pushes the rib cage out sideways and forwards. This will result in pain in the front of the lower ribs, also known as ribflare. Furthermore, rib-flaring makes expectant women breathe with the top part of her chest. This causes breathlessness even during mild exertion during pregnany but especially so, towards the end of term.

Cardiovascular System

During pregnancy, a woman’s blood volume increases by at least 40%. However, the plasma volume increases more than the red cells, hence possibly resulted in dilution anaemia, leading to tiredness in the early weeks of pregnancy. She may also feel faint when lying on her back. This is due to enlarging fetus compressing the aorta and inferior vena cava against the lumbar spine, thereby restricting blood flow. This condition is known as pregnancy supine hypotensive syndrome. Turning onto her side can relieve the symptoms. Such a condition tends to happen more in the 3rd trimester. However, it can also occur any time after the 4th month of pregnancy.

Varicose veins of the legs may occur during pregnancy or worsen during this period. This is due to reduction in vascular tone and changes in collagen structure in the body (due to progesterone and relaxin) .

For the same reason, “water retention” or swelling in ankles, feet and hands in late pregnancy may lead to joint stiffness and nerve compression syndromes. Examples include carpal tunnel syndrome.

Musculoskeletal System

The hormone, relaxin, is produced about 2 weeks into pregnancy. Relaxin alters the composition of collagen, which exist in joints, ligaments and connective tissues. As a result, the modified collagen is more elastic and flexible. This leads to more movement in joints, and thus less stability of the system. The weight bearing joints, such as the pelvis, bear the brunt of the increased stress and loading during pregnancy. And with the instability that relaxin cause, the pelvis is susceptible to injury and pain, one of the conditions known as symphysis pubis diastasis. Also, ligaments of feet become lax and with the additional weight of pregnancy, causes discomfort. This results in aching and flat feet. Hence, comfortable and supportive foot wear is strongly recommended during this period.

Posture-wise, her centre of gravity will move forward. This leads to increased lower back curvature, compensatory curving of the upper back, rounding of shoulders and forward chin position. This incorrect posture exerts excessive strain and fatigue on her body, particularly on the spine, pelvis and other weight bearing joints (i.e. knees). This will result in aches and pains, with the pain spreading to the buttocks, thighs and down the legs.

Other muscular changes, such as the separation of the abdominal muscle, known as recti diastasis, are associated with low back strain. This is because the abdominals are no longer able to support core and the spine as efficiently as before.


With all the extensive changes in the expectant woman’s body, it is obvious that the healtier and fitter she is both before and during pregnancy, the more easily she can cope with pregnancy. Before each pregnancy, she should prepare to be fit physically and emotionally, and maintain the fitness during the pregnancy. This will enhance recovery after delivery. The next article in this series will focus on common physical problems affecting women during pregnancy, and its solutions.