physical changes during pregnancy

Physical Changes During Pregnancy and how prenatal yoga helps with these changes

The maternal changes in pregnancy are due to hormonal changes and mechanical effects of the enlarging baby and uterus. The major hormones are oestrogen (the hormone of growth) and progesterone (the hormone affecting function). Both hormones are produced initially by the ovaries and later by the placenta in increasing quantities throughout the pregnancy. The changes occur gradually over the duration of pregnancy which is usually about 266 days from conception or 280 days after last menstrual period assuming a 28 day cycle (i.e. ovulation occurs on day 14).


There is a massive enlargement of the uterus which increases in length from about 8cm to 30cm by term and in weight from 50gm to 1000gm with a capacity over 500 times greater. These changes are associated with muscle fibre growth and enlargement of the blood vessels and are initially due to hormonal influences, but later are partly mechanical caused by the growing baby, placenta and amniotic fluid. As the uterus enlarges it changes from a pear shape to oval and back to pear shaped again near term. With this enlargement the uterus grows out of the pelvis entering the abdomen to displace intestines to the sides and eventually coming in contact with the abdominal wall and under surface of the liver. It also becomes both tilted and slightly rotated to the right side, possibly due to the presence of the rectum on the left side. This enlargement may lead to pressure on intra abdominal organs and contribute to a number of the discomforts associated with pregnancy such as bladder symptoms, constipation, gastric reflux and breathing difficulties due to pressure under the diaphragm. There is a large increase in uterine and placental blood flow amounting to about 500ml per minute at term. The cervix softens and a mucus plug forms in the cervical canal to prevent ascent of bacteria, which could cause infection.

Prenatal yoga will help ease some of the physical discomforts of the baby growing, by creating space for the mother and baby both physically and emotionally. Yoga will help the mother feel more confidant and at peace with the changes taking place in her body.

Other Changes

Abdominal Wall distension leads to flattening and finally protrusion of the umbilicus and the skin may develop striae (stretch marks) which may partly be due to stretching, but are also due to hormonal changes (adrenocortical steroids from the adrenal glands) . In some women abdominal wall stretching leads to separation of the 2 longitudinal midline rectus muscles (diastasis recti).

Breast Changes in preparation for lactation are largely hormonally driven and result in breast enlargement and deep pigmentation of the areola which also develop enlarged sebaceous glands known as Montgomery follicles. Production of colostrum begins in the latter stages of pregnancy. Pigment may also be deposited in the midline of the abdomen (linea nigra) and on the face (pregnancy mask or chloasma).

Musculoskeletal Changes occur as a result of hormonal influences such as relaxin which causes a softening of ligaments and hence a laxity of joints particularly in the pelvis which facilitates the easier passage of the baby through the pelvis at delivery. In combination with the postural changes associated with enlarging uterus this can sometimes lead to stresses in the spinal column and backache. Gentle yoga postures practiced regularly can help establish a better posture throughout the pregnancy and ease some of the aches and pains associated with the pregnancy.

Gastrointestinal Tract

During pregnancy nutritional requirements, including those for vitamins and minerals, are increased and several maternal alterations occur to meet this demand. The appetite usually increases, so that food intake is greater although some women have a decreased appetite or experience nausea and vomiting. These symptoms may be related to increasing levels of human chorionic gonadotrophin (HCG) and oestrogen, as well as mechanical factors in late pregnancy.

It is important to try and eat as healthily as possible during pregnancy and there is much information on diet available through orthodox or alternative medicine practitioners.

Gastrointestinal Motility

Gastrointestinal motility is reduced during pregnancy due to increased levels of progesterone. Transit time of food throughout the gastrointestinal tract may be so much slower that more water than normal is reabsorbed leading to constipation.

Certain pregnancy yoga poses like squatting, or wide legged standing poses, help maintain regular bowel movements.

Stomach and Oesophagus

Gastric production of mucus may be increased. Oesophageal peristalsis is decreased and accompanied by gastric reflux due to slower gastric emptying time and dilatation or relaxation of the cardiac oesophageal sphincter. Gastric reflux is more common in later pregnancy owing to elevation of the stomach by the enlarged uterus.

Yoga postures that help lengthen the spine and lift the rib cage up and away from the baby maybe helpful during times of reflux.

Haematological System

Blood Volume `

The blood volume increases on average by 30 -40%. The increase is needed for extra blood flow to the uterus, extra metabolic needs of baby and increased perfusion of others organs. Extra volume also compensates for maternal blood loss at delivery.

Red and White Blood Cells

The increase in blood volume is associated with a similar increase in red and white blood cells.

With the increase in red blood cells, the need for iron for the production of haemoglobin increases. If supplemental iron is not added to the diet, iron deficiency anaemia may result. If iron is not readily available, the baby uses iron from maternal stores.

Cardiovascular System

As the uterus enlarges and the diaphragm becomes elevated, the heart is displaced upward and somewhat to the left. Cardiac output increases approximately 30% during pregnancy, reaching a maximum at 26 -28 weeks gestation and continuing at this level until term.

The blood pressure declines slightly during pregnancy.

Partial obstruction of the inferior vena cava by the enlarging uterus can result in decreased blood return to the heart. This may decrease cardiac output leading to a fall in blood pressure and cause fainting, particularly when lying on the back (‘supine hypotension’) and is relieved by lying on the side.

If you have low blood pressure it is unadvisable to move the body up and down too much during a prenatal yoga class or to stand for too long, using a chair maybe helpful with some of the poses.

Respiratory System

Pregnancy produces anatomic and physiologic changes that affect respiratory function. Early in pregnancy capillary dilatation occurs throughout the respiratory tract, leading to engorgement of the nasopharynx, larynx, trachea, and bronchi. This causes the voice to change and makes breathing though the nose difficult. As the uterus enlarges, the diaphragm is elevated and the rib cage is displaced upward and widens. Elevation of the diaphragm does not impede its movement, but abdominal muscles have less tone and are less active during the pregnancy, causing breathing to be more diaphragmatic.

Prenatal yoga will help with breath shortness during pregnancy by the practice of pranayama which will help the women to consciously slow down her breath by the use of ujjayi breath. During the yoga practice it is encouraged to breath out through the mouth if that is more easy for the expectant mum.

Metabolic Changes

As the baby and placenta grow and place increasing demands on the mother, many alterations in metabolism occur. The most obvious physical changes are weight gain and altered body shape. Weight gain is due not only to the uterus and its contents but also to increased breast tissue, blood and water volume in the form of extravascular and extracellular fluid and fat and protein stores.

Weight Gain is due to a combination fluid retention, fat and protein and gaining weights of the baby, uterus, placenta and amniotic fluid. Weight gain is extremely variable during pregnancy.

Fluid retention is associated with a large increase in the blood volume (30%) by the end of pregnancy as well as an increase tissue fluid throughout the body, but particularly in the uterus, breasts and legs.

By attending a regular prenatal yoga class the expectant mother will practice certain poses that will help her to feel lighter and more energised, and help maintain a healthy weight gain throughout the pregnancy.

Protein Metabolism is associated with a positive nitrogen balance. Protein is used for the development of the baby, uterus and breasts and is stored for the production of milk.

Fat Metabolism is associated with increasing absorption of fat, lecithin and cholesterol particularly towards the end of pregnancy to lay down subcutaneous tissue in the baby and to prepare for lactation in the mother.

Carbohydrate Metabolism. Sugar is more likely to appear in the urine (glycosuria) in pregnancy and is probably related to a change in renal function rather than significantly altered carbohydrate metabolism.

Minerals. There is a positive balance of calcium, phosphate, iron, magnesium, chloride, potassium and sodium. The developing baby requires significant amounts of calcium, phosphate and iron as does the mother for lactation and the increasing blood volume.

The majority of this article was written by Don Rawling who practiced as an obstetrician/gynaecologist in Melbourne for well over 30 years, delivering lots of healthy happy baby’s into the world.