Pregnancy normally lasts about 40 weeks and is grouped into three stages, or trimesters.

 

  • Weight Gain During Pregnancy
    • an average of 25 to 27 lbs
  • Changes in Musculoskeletal System
    • Abdominal muscles
      • Both sides of the rectus, are stretched to the point of their elastic limit by the end of pregnancy
      • Shift in the center of gravity also decreases the mechanical advantage of the abdominal muscles
    • Pelvic floor muscles
      • In their anti-gravity position, must withstand the total change in weight; the pelvic floor drops as much as 2.5 cm (1 inch) as a result of pregnancy
    • Connective tissues and joints
      • The thoracolumbar fascia is put in a position of extreme length, which diminishes its ability to stabilize the trunk effectively
      • Joint hypermobility occurs as a results of ligamentous laxity
  • Changes in Posture and Balance
    • Center of Gravity
      • COG shifts upward and forward because of the enlargement of the uterus and breasts
      • The lumbar and cervical lordosis increase, knee hyperextend
      • The shoulder girdle and upper back become rounded with scapular protraction and upper extremity internal rotation because of breast enlargement; this postural tendency persists with postpartum positioning for infant care
      • The suboccipital muscles; moderate forward head posture along with the change in shoulder alignment
      • Weight shifts toward the heels to bring COG to a more posterior position; this contributes to the “waddling” gait that is typical seen in pregnancy
    • Balance
      • Walks with a wider base of support and increased external rotation at the hips
  • Cardiovascular System
    • Blood volume and pressure
      • Progressively increased 35% to 50% (1.5 to 2 liters) throughout pregnancy and returns to normal by 6 to 8 weeks after delivery
      • Plasma increase is greater than red blood cell increase, leading to the “physiologic anemia”
      • Venous pressure in the lower extremities increases during standing as a result of increased uterine size and increased venous distensibillity.
      • Pressure in the inferior vena cava rises in late pregnancy, especially in the supine position, because of compression by the uterus just below the diaphragm: decline in venous return and resulting decrease in cardiac output may lead to symptomatic supine hypotensive syndrome.
      • The aorta is partially occluded in the supine position
      • First trimester: slight dec. of systolic pressure, greater dec. of diastolic pressure
      • BP reaches its lowest level approximately midway
      • BP rises from mid-pregnancy to reach the pre-pregnant level approximately 6 weeks after delivery.
    • Heart
      • Heart rhythm disturbances are more common during pregnancy
      • Increase 10 to 20 beats per minute
      • Returns to normal levels within 6 weeks after delivery
      • Cardiac output increases 30% to 60 % during pregnancy
      • Most significantly increased when a woman is in the left side-lying position, in which the uterus places the least pressure on the aorta.
  • Urinary System
    • Kidneys
      • Increase in length by 1 cm (0.5 inch)
    • Ureters
      • The ureters enter the bladder at a perpendicular angle because of uterine enlargement
      • Result in a reflux of urine out of the bladder and back into the ureter
      • Increased chance of developing urinary tract infections because of urinary stasis
  • Pulmonary System
    • Hormonal influences
      • Pulmonary secretions and rib cage position
      • Edema and tissue congestion of the upper respiratory tract begin early in pregnancy
      • Changes in rib position are hormonally stimulated and occur prior to uterine enlargement
      • The subcostal angle progressively increases; the ribs flare up and out
      • Diaphragm is elevated by 4cm (1.5 inch); this is a passive change cased by the change in rib position
    • Respiration
      • Tidal volume and minute ventilation increase, but total lung capacity is unchanged or slightly decreased.
      • 15% to 20% increase in oxygen consumption: a natural state of hyperventilation exists throughout pregnancy to meet the oxygen demands
      • The work of breathing increases because of hyperventilation; dyspnea is present with mild exercise as early as 20 weeks into the pregnancy