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8/8/2019 Adaptations to Pregnancy
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Physiologic Adaptations toPregnancy
E.S.Prakash
Faculty of Medicine
AIMST University
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Intended learning outcome:
At the end of this lecture, we should be able to
Briefly describe the physiologic changes in
various organs and organ systems(cardiovascular, respiratory, gastrointestinal,
uterine, hematological) that occur during
pregnancy, and explain the underlying
mechanisms (wherever known).
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Changes in Reproductive Tract:
Uterus:
Progressive increase in size and thickness of
uterus Enlargement involves stretching and
hypertrophy of smooth muscle cells
Irregular painless uterine contractions calledraxton-Hicks contractions (first trimester
onward)
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Uteroplacental blood flow
Increases to about 450-650 ml/min at term;
Resistance to blood flow in the uterus and placentadecreases considerably because of the effects of
estrogen
Changes in uterine cervix -
Cervix becomes soft, produces copious amounts of
mucus that can plug the cervical canal; details can
be studied later;
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Ovaries
Ovulation ceases
Maturation of new follicles suspended Corpus luteum of pregnancy critical until
about the 8th week for sustaining pregnancy
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Haematological changes
Increase in blood volume due to an increase in RBC
volume as well as plasma volume
However, plasma volume increases much more
Thus, packed cell volume drops (i.e., because of
hemodilution)
Also called physiologic anaemia ofpregnancy
However, a drop in Hb levels below 11 g/dL shouldbe considered abnormal.
Iron requirements increase (dietary supplementation
necessary)
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Leukocyte count is slightly elevated
During labour, it may increase to as high as
25000 per microlitre Erythrocyte sedimentation rate (ESR) is
increased because of an increase in plasma
levels of globulins and fibrinogen
Pregnancy is characterized by increased levels
of most clotting factors
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Cardiovascular
Changes in
Pregnancy (and theeffects of posture on
it)
Note the increase in
resting heart rate
Stroke volume
initially increases and
then decreasestoward term
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Cardiac output in pregnancy
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Changes in arterial blood pressure
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Changes in cardiac outline in
pregnancyColored lines
indicate the
nonpregnant
state
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Pulmonary function
Respiratory rate changes little
Tidal volume increases
Maximal voluntary ventilation not appreciablyaltered
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Renal changes;
urinary tract changes Increase in the size of kidneys
Increase in glomerular filtration rate
Increase in renal plasma flow
Increase in clearance of creatinine..
Glycosuria not necessarily abnormal..
Dilation of renal pelvicalyceal system
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Normal intravenous
pyelogram inpregnancy
Note the dilated renal
pelvicalyceal systemand the dilated ureter
on the right side
(arrows)
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Gastrointestinal changes
Displacement of stomach and intestines by the
enlarging uterus..
Gastric emptying time essentially unchanged
during pregnancy but increased at the time of
labour..
Heartburn due to gastro-oesophageal reflux
quite common
Haemorrhoids quite common (reason -
pressure effects of an enlarged uterus)
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Gastrointestinal changes contd.
Gall bladder contractility reduced..effect of
progesterone??
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Endocrine function during
pregnancy Pituitary gland enlarges by about 135%
Plasma levels of prolactin increase about 10
fold
Moderate enlargement of thyroid gland is
common
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Reference:
Chapter on Maternal Physiology in Williams
Obstetrics, Mc Graw Hill.
Access at http://www.accessmedicine.comusing institutional log in ID