Physiological changes during pregnancy

Original Editor - Esraa Mohamed Abdullzaher

Top Contributors - Esraa Mohamed Abdullzaher  


Muscles , Joints and bones

The pelvis is the region found between the trunk and lower limbs. In females, the pelvis is wider and lower than that of their male counterpart, making it more suited to accommodate a fetus during both pregnancy and delivery[1]. It protects and supports the pelvic contents, provides muscle attachment and facilitates the transfer of weight from trunk to legs in standing, and to the ischial tuberosities in sitting.

The cross-sectional anatomy of the female pelvis shows five bones: two hip bones, sacrum, coccyx and two femurs. Each hip bone is formed by the fusion of three bones: the ilium, pubis and ischium. The sacrum and coccyx are also comprised of smaller bones. The first is formed by the fusion of the five sacral vertebrae (S1-S5), and the latter by the fusion of the four coccygeal vertebrae. The femur articulates with the hip, forming the ball-and-socket hip joint.[1]

The joints are supported by some of the strongest ligaments in the body which become more lax during pregnancy leading to increased joint mobility and less efficient load transfer through the pelvis. The pelvic outlet at the base of the pelvis is narrower in transverse diameter when compared with the pelvic inlet; it comprises the pubic arch, ischial spines, sacrotuberous ligaments and coccyx.[2]

Four pairs of abdominal muscles combine to form the anterior and lateral abdominal wall, and may be termed the abdominal corset. Transversus abdominis lies deep to the internal abdominal oblique and external abdominal oblique with the rectus abdominis central, anterior and superficial IO, EO and TrA insert into an aponeurosis joining in the midline at the linea alba. The deep abdominal muscles, together with the pelvic floor muscles, multifidus and diaphragm, can be considered as a complete unit and may be termed the lumbopelvic cylinder. This provides support for the abdominal contents and maintains intra­abdominal pressure. The main function of RA is lumbar spine flexion while the obliques produce side­flexion and rotation of the spine.[2]

The muscles of the back region include the quadratus lumborum, latissimus dorsi, serratus posterior inferior, erector spinae, interspinales and transversospinalis muscles.The muscles present in the thigh region can be split into three sections, anterior, medial and posterior.

The anterior compartment is comprised of the iliopsoas, quadratus femoris, sartorius, and pectineus. The medial compartment is comprised of the adductor magnus, adductor longus, adductor brevis, obturator externus, and gracilis. The posterior compartment is comprised of the biceps femoris, semitendinosus and semimembranosus muscles. In the gluteal region, the muscles seen there are the gluteus maximus, gluteus medius, gluteus minimus and tensor fascia latae, as well as the deeper piriformis, gemellus superior, gemellus inferior and obturator internus muscles.

The pelvic floor includes the levator ani, bulbospongiosus and the deep transverse perineal muscles.[1]

female reproductive system

Organs of the female reproductive system present in the pelvis are subdivided into internal and external genitalia. The internal genitalia consist of the uterus, two uterine tubes, two ovaries and the vagina. The external genitalia, mainly consist of the mons pubis, clitoris, labia majora and minora, and Bartholin glands.[1]

Musculoskeletal changes during pregnancy

Postural changes

The overall equilibrium of the spine and pelvis alters as pregnancy progresses but there is still confusion as to the exact nature of any associated postural adaptation. With weight gain, increased blood volume and ventral growth of the fetus, the centre of gravity no longer falls over the feet and women may need to lean backwards to gain equilibrium resulting in disorganisation of spinal curves. Reported postures include a reduction in lumbar lordosis an increase in both lumbar lordosis and thoracic kyphosis or a flattening of the thoracolumbar spinal curve. There will be compensatory changes to posture in the thoracic and cervical spines, and this combined with the extra weight of the breasts may result in posterior displacement of the shoulders and thoracic spine, and increase of the cervical lordosis.[2]

Articular changes

Altered levels of relaxin, oestrogen and progesterone during pregnancy result in an alteration to collagen metabolism and increased connective tissue pliability and extensibility. Therefore, ligamentous tissues are predisposed to laxity with resultant reduced passive joint stability. The symphysis pubis and sacroiliac joints are particularly affected to allow for birth of the baby. Ligamentous laxity may continue for six months postpartum. Biomechanical changes of the spinal and pelvic joints may involve an increase in sacral promontory, an increase in lumbosacral angle, a forward rotatory movement of the innominate bones, and downward and forward rotation of the symphysis pubis. The normal pubic symphyseal gap of 4–5 mm shows an average increase of 3 mm during pregnancy . Pelvic joint loosening begins around 10 weeks, with maximum loosening near term. Joints should return to normal at 4–12 weeks postpartum .The sacrococcygeal joints also loosen. By the last trimester, the hip abductors and extensors, and the ankle plantarflexors increase their net power during gait and there is an increase in load on the hip joints of 2.8 times the normal value when standing and working in front of a worktop . As the uterus rises in the abdomen the rib cage is forced laterally and the diameter of the chest may increase by 10–15 cm .[2]

Neuromuscular changes

During pregnancy the enlarged uterus results in elongation of the abdominal muscles and separation of the linea alba. Passive joint instability (as seen in pregnancy) alters afferent input from joint mechanoreceptors and probably affects motor neurone recruitment. A decrease in muscle stiffness and thus active stability of joints may result from alteration of muscle spindle regulation and this is applicable particularly to muscles around the pelvic girdle. These changes may lead to poor recruitment of the muscles responsible for pelvic girdle stability (particularly gluteus medius and maximus) and result in decreased tension of these muscles during walking, perhaps resulting in pelvic girdle pain (PGP).[2]

Cardiovascular changes

The heart adapts to the increased cardiac demand that occurs during pregnancy in many ways. Cardiac output increases throughout early pregnancy, and peaks in the third trimester, usually to 30-50% above baseline. Estrogen mediates this rise in cardiac output by increasing the pre-load and stroke volume, mainly via a higher overall blood volume (which increases by 40–50%). The heart rate increases, but generally not above 100 beats/ minute. Total systematic vascular resistance decreases by 20% secondary to the vasodilatory effect of progesterone. Overall, the systolic and diastolic blood pressure drops 10–15 mm Hg in the first trimester and then returns to baseline in the second half of pregnancy. All of these cardiovascular adaptations can lead to common complaints, such as palpitations, decreased exercise tolerance, and dizziness.[3]

Gastrointestinal changes

Progesterone causes smooth muscle relaxation which slows down GI motility and decreases lower esophageal sphincter (LES) tone. The resulting increase in intragastric pressure combined with lower LES tone leads to the gastroesophageal reflux commonly experienced during pregnancy.Nausea and vomiting of pregnancy, commonly known as “morning sickness”, is one of the most common GI symptoms of pregnancy. It begins between the 4 and 8 weeks of pregnancy and usually subsides by 14 to 16 weeks. The exact cause of nausea is not fully understood but it correlates with the rise in the levels of human chorionic gonadotropin, progesterone, and the resulting relaxation of smooth muscle of the stomach[3].also constipation and hemorroids can occur during pregnancy.

Renal changes

A pregnant woman may experience an increase in the size of the kidneys and ureter due to the increase blood volume and vasculature. Later in pregnancy, the woman might develop physiological hydronephrosis and hydroureter, which are normal.


During pregnancy, both protein metabolism and carbohydrate metabolism are affected. One kilogram of extra protein is deposited, with half going to the fetus and placenta, and another half going to uterine contractile proteins, breast glandular tissue, plasma protein, and haemoglobin. An increased requirement for nutrients is given by fetal growth and fat deposition. Changes are caused by steroid hormones, lactogen, and cortisol.Pregnant women require a caloric increase.also there's a weight gain of 20 to 30 lb (9.1 to 13.6 kg) .[3]

Problems may have during pregnancy

1-Pelvic floor dysfunction.

2-Symphysis pubis dysfunction.

3-Rib pain.

4-Nerve compression syndromes.

5-back pain.

6-carpal tunnel syndrome.

7-muscle cramps.

8-morning sickness.


Exersices and contraindications for it

For regular exercisers Consult your doctor or midwife before beginning exercise.

Exercise at a moderate level most days for 30 minutes or more also discontinue contact sports and activities which carry a high risk of falling or abdominal trauma. Avoid scuba diving.

Self­regulate both the level of intensity and duration of exercise, aiming to keep core temperature below 38°C.and aim for low impact activity..Wear suitably supportive footwear to reduce musculoskeletal stresses.Maintain adequate fluid intake to prevent dehydration, and avoid exercise during hot and humid weather, or with pyrexia. Warm­up and cool­down for at least five minutes. Do not use developmental stretching (because of the effects of relaxin).

Seek professional advice on specific exercises (e.g. for the pelvic floor muscles). Avoid ballistic exercise, low squats, crossover steps and rapid changes of direction.Do not exercise in supine after 16 weeks gestation, to avoid aortocaval compression. Eat to appetite, without calorific restriction.Work towards cross­training to avoid over­training, and stop exercise before fatigue sets in.

In addition to the above, women not used to regular exercise should be advised:

not to start an exercise programme until >13 weeks gestation; to consider beginning with non­weight­bearing exercises, such as aquanatal classes; to progress from simple and basic levels of exercise, increasing exercise tolerance gradually, under the supervision of a suitably qualified professional.

Contraindications to exercise include:

cardiovascular, respiratory, renal or thyroid disease; diabetes (type 1, if poorly controlled); history of miscarriage, premature labour, fetal growth restriction, cervical incompetence; hypertension, vaginal bleeding, reduced fetal movement, anaemia, breech presentation, placenta praevia.[2]

All women should stop exercising immediately and seek advice from a doctor if they experience: abdominal pain.per vaginum (from the vagina) bleeding.shortness of breath, dizziness, faintness, persistent severe headache, palpitations or tachycardia; PGP, which may also lead to difficulty in walking.

See also

Pregnancy Related Pelvic Pain

Low Back Pain and Pregnancy


  1. 1.0 1.1 1.2 1.3
  2. 2.0 2.1 2.2 2.3 2.4 2.5 Stuart Porter,Tidy's physiotherapy.1991
  3. 3.0 3.1 3.2