adaptations to pregnancy

8/8/2019 Adaptations to Pregnancy

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Physiologic Adaptations toPregnancy

E.S.Prakash

Faculty of Medicine

AIMST University

[email protected]


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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

adaptations to pregnancy

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