ANATOMICAL AND PHYSIOLOGICAL CHANGES OF PREGNANCY
Weight Gain During
Pregnancy
·
Current recommendations for weight gain
during pregnancy are an average of 25 to 27 lbs.
|
Fetus
3.36–3.88 kg (7.5–8.0 lb) Placenta
0.48–0.72 kg (1.0–1.5 lb) Amniotic
fluid 0.72–0.97 kg (1.5–2.0 lb) Uterus
and breasts 2.42–2.66 kg (5.0–5.5 lb) Blood and fluid 1.94–3.99 kg (4.0–7.0 lb) Muscle
and fat 0.48–2.91 kg (1.0–6.0 lb)) |
|
Total:
9.70–14.55 kg (20.0–30.0 lb |
Changes in Organ Systems
Uterus and Related
Connective Tissue
Uterus
·
The uterus increases from a prepregnant
size of 5 by 10 cm (2 by 4 inches) to 25 by 36 cm (10 by 14 inches).
·
It increases five to six times in size,
3000 to 4000 times in capacity, and 20 times in weight by the end of pregnancy.
·
By the end of pregnancy, each muscle cell
in the uterus has increased approximately 10 times over its pre-pregnancy
length.
·
Once the uterus expands upward and leaves
the pelvis, it becomes an abdominal rather than a pelvic organ.
Connective tissues
·
Ligaments connected to the pelvic organs
are more fibroelastic than ligaments supporting joint structures.
·
The fascial tissues, which surround and
enclose the organs in a continuous sheet, also include a significant amount of
smooth muscle fibers.
· The round, broad, and uterosacral ligaments in particular provide suspensory support for the uterus.
Urinary System
Kidneys
·
The kidneys increase in length by 1 cm
(0.5 inch).
Ureters
·
The ureters enter the bladder at a
perpendicular angle because of uterine enlargement. This may result in a reflux
of urine out of the bladder and back into the ureter; therefore, during
pregnancy there is an increased chance of developing urinary tract infections
because of urinary stasis.
Pulmonary System
Hormonal influences
·
Hormone changes affect pulmonary
secretions and rib cage position.
·
Edema and tissue congestion of the upper
respiratory tract begin early in pregnancy because of hormonal changes.
·
Hormonally stimulated upper respiratory
hypersecretion also occurs.
·
Changes in rib position are hormonally
stimulated and occur prior to uterine enlargement.
·
The subcostal angle progressively
increases; the ribs flare up and out.
·
The anteroposterior and transverse chest
diameters each increase by 2 cm (1 inch). Total chest circumference increases
by 5 to 7 cm (2 to 3 inches) and does not always return to the pre-pregnant
state.
·
The diaphragm is elevated by 4 cm (1.5
inch); this is a passive change caused by the change in rib position.
Respiration.
·
Respiration rate is unchanged, but depth
of respiration increases.
·
Tidal volume and minute ventilation
increase, but total lung capacity is unchanged or slightly decreased.56,66
There is a 15% to 20% increase in oxygen consumption; a natural state of
hyperventilation exists throughout pregnancy to meet the oxygen demands of
pregnancy.
·
The work of breathing increases because of
hyperventilation; dyspnea is present with mild exercise as early as 20 weeks
into the pregnancy.
Cardiovascular System
Blood volume and
pressure.
·
Blood volume progressively increases 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” of pregnancy, which is not a
true anemia but is representative of the greater increase of plasma volume.
·
The increase in plasma volume occurs as a
result of hormonal stimulation to meet the oxygen demands of pregnancy.
·
Venous pressure in the lower extremities
increases during standing as a result of increased uterine size and increased
venous distensibility.
·
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. In some women, the 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. Blood pressure decreases early in the first trimester.
·
There is a slight decrease of systolic
pressure and a greater decrease of diastolic pressure.
·
Blood pressure reaches its lowest level
approximately midway through pregnancy, then rises gradually from mid-pregnancy
to reach the pre-pregnant level approximately 6 weeks after delivery.
·
Although cardiac output increases, blood
pressure decreases because of venous distensibility.
Heart
·
Heart size increases, and the heart is
elevated because of the movement of the diaphragm. Heart rhythm disturbances
are more common during pregnancy.
·
Heart rate usually increases 10 to 20
beats per minute by full term and returns to normal levels within 6 weeks after
delivery.
·
Cardiac output increases 30% to 60% during
pregnancy and is most significantly increased when a woman is in the left
side-lying position, in which the uterus places the least pressure on the
aorta.
Musculoskeletal System
Abdominal muscles.
·
The abdominal muscles, particularly both
sides of the rectus, are stretched to the point of their elastic limit by the
end of pregnancy.
·
This greatly decreases the muscles’
ability to generate a strong contraction, and thus decreases their efficiency
of contraction.
·
The shift in the center of gravity also
decreases the mechanical advantage of the abdominal muscles.
Pelvic floor muscles
·
The 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 hormonal influence on the ligaments is
profound, producing a systemic decrease in ligamentous tensile strength.
·
This change is primarily a result of an
increase in relaxin and progesterone levels.
·
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 result of
ligamentous laxity and may predispose the patient to injury, especially in the
weight-bearing joints of the back, pelvis, and lower extremities.
Thermoregulatory System
Metabolic rate
·
During pregnancy, basal metabolic rate and
heat production increase.
·
An additional intake of 300 calories per
day is needed to meet the basic metabolic needs of pregnancy.
·
In pregnant women, normal fasting blood
glucose levels are lower than in nonpregnant women.
Changes in Posture and
Balance
Center of Gravity
·
The center of gravity shifts upward and
forward because of the enlargement of the uterus and breasts.
·
This requires postural compensations to
maintain balance and stability.
·
The lumbar and cervical lordoses increase
to compensate for the shift in the center of gravity, and the knees
hyperextend, probably because of the change in the center of gravity.
·
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.
·
Tightness of the pectoralis muscles and
weakness of the scapular stabilizers may be preexisting to or perpetuated by
the pregnancy postural change.
·
The suboccipital muscles respond in an
effort to maintain appropriate eye level (optical righting reflex), and to
moderate forward head posture along with the change in shoulder alignment.
·
Weight shifts toward the heels to bring
the center of gravity to a more posterior position.
·
This contributes to the “waddling” gait
that is typically seen in pregnancy.
·
Changes in posture do not automatically
correct after childbirth, and the pregnant posture may become habitual.
·
In addition, many child-care activities
contribute to persistent postural faults and asymmetry.
Balance
·
Balance with the increased weight and
redistribution of body mass there are compensations to maintain balance.
·
The pregnant woman usually walks with a
wider base of support and increased external rotation at the hips.
·
This change in stance along with growth of
the baby makes some activities such as walking, stooping, stair climbing,
lifting, reaching, and other activities of daily living (ADLs) progressively
more challenging.
·
Activities requiring fine balance and
rapid changes in direction, such as aerobic dancing and bicycle riding, may
become inadvisable, especially during the third trimester
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