Dr. bashiir macalin maxamuud MBBS

1. PHYSIOLOGICAL CHANGES
OF
PREGNANCY

2. I. OBJECTIVES
At the end of this session you should be able to:
1. Describe the normal distribution of body fluids
2. Decribe the changes in body fluids during
pregnancy
3. Outline the physiological changes in various
systems during pregnancy
4. Distinguish physiological versus pathologic
changes during pregnancy
5. Diagnostic tests and interpretations during
pregnancy

3. I. BODY FLUIDS WITHOUT PREGNANCY
Total body water
• Average normal weight = 70kg
• 60% of bwt is water = 42L
• Distribution in the fluid compartments
– ⅔ ICV = 28L
– ⅓ ECV = 14L
–¾ interstitial = 10.5L
–¼ intravascular = 3.5L

4. BODY FLUID CHANGES IN PREGNANCY
• Body Fluid - ↑ by 6-8 L
• ⅔ of this increase is extravascular
especially IVFV
• Causes of fluid retention
1.Placenta produces renin which then activates
RAAS
• This causes increased Na+ and H2O
reabsorption in the kidneys
2.Oestrogen has some glucocortocoid activities
that enhance reabsorption of Na+ and H2O

5. BODY FLUIDS AND WEIGHT GAIN
Weight gain
Total normal wt gain 7- 17 kg, average 12.5kg
• Blood =1.5kg
• Extravascular fluid =1.5kg
• Uterus =1.0 kg
• Placenta = 0.5 – 0.7 kg
• Fetus = 3.4kg
• Amniotic fluid = 0.8kg
• Breast = 0.5 kg
• Other stores (fat) = 3.3kg
Note: Appetite ⇈ [effects of estrogen on the appetite
center]

6. HAEMATOLOGICAL CHANGES
• Plasma volume increases by 45 - 50%
– Beginning by the 6th wk
• RBC mass increases by 20-35%
– Moderate erythroid hyperplasia in bone marrow
– Beginning by the 12th wk but more marked after 20 wks
• Disproportionate increase in plasma volume over
RBC volume -- Hemodilution [Physiological anaemia
of pregnancy]
– Despite erythrocyte production there is a physiologic fall
in the hemoglobin and hematocrit readings

7. Iron deficiency anemia
• With erythropoiesis of pregnancy, iron
requirements increase.
• Because large amounts of iron may not be
available from body stores and may not be
in the diet
– Supplementation is recommended to prevent
iron deficiency anemia
– At term, Hemoglobin less than 10.0 is usually
due to iron deficiency anemia rather than the
hemodilution of pregnancy

8. Cardiovascular system
1. CARDIAC OUTPUT (CO) = HR X SV
• CO increase 30-50%
– Initial increase is a function of
• The increase in heart rate (10-20%)
• Reduced systemic vascular resistance by
35%
• By 10- 20 wks the increase in CO is reflected
mainly by the increase in SV
– Fluid retention →↑ECFV →↑SV →↑CO
– The notable increase in plasma volume or
preload contributes to the increase SV

9. As pregnancy advances to term
• The HR continues to increase but the SV falls to
close to normal levels.
• This accounts for the fall in CO to near non-pregnant
levels at term
2. HEART SOUNDS
– ↑ loudness of S1 & S2, S3
– Diastolic murmur in 20%,

10. 3. BLOOD PRESSURE
• Normally: slight decrease in DBP > ↓ SBP
• Despite ↑ CO and ↑ plasma volume
• Indicates significant ↓ peripheral
resistance

11. Interpretation of tests in pregnancy
i. CXR
• Elevation of diaphragm
• Heart to be displaced to the left and upward
• Increase in the cardiac silhouette
• Benign pericardial effusion
ii. Echocardiogram
• Increased left ventricular wall mass
• Increased end diastolic dimensions
• Increase in EDV( end-diastolic volume) and
therefore ⇈in SV
iii. Electrocardiogram
• Slight left axis deviation

12. ESPIRATORY SYSTEM
1. Mechanical changes
Diaphragm rises up to 4 cm
– Less negative intrathoracic pressure
– ↓Functional Residual Capacity (FRC)
• volume after passive expiration
– ↓Expiratory Reserve Volume (ERV)
• max volume expired after passive expiration
– ↓ Residual Volume (RV)
• volume after max expiration
• No impairments in diaphragmatic or thoracic muscle
motion
– Lung compliance remains unaffected

13. CONT. RESPIRATIORY
2. Consumption
• O2 consumption increases by 15-20 %
• 50 % of this increase is required by the uterus.
• Despite increase in oxygen requirements, with the
increase in Cardiac Output and increase in alveolar
ventilation oxygen consumption exceeds the
requirements.
• Therefore, arteriovenous oxygen difference falls and
arterial PCO2 falls.

14. RESPIRATIORY cont
3. Stimulation
• Progesterone is known to directly stimulate
ventilation
• Progesterone increases the sensitivity of the
respiratory center to CO2
• Also, it is thought to reduce total pulmonary
resistance
– Effects of progesterone on smooth
muscles

15. RESPIRATIORY cont
• Physiologic changes
Dyspneoa - increase in desire to breath
– 70 % of pregnant women experience this
– Occurs during 1st trimester without mechanical
factors
– The lower PCO2 then paradoxically causes dyspneoa
– The marked change or marked decline in PCO2
results in the sensation of dyspneoa

16. REPORODUCTIVE SYSTEM
CHANGES
• Increased vascularity and hyperemia
– Vagina, perineum and vulva
• Increased secretions
• Blue coloration of the vagina
– Chadwick’s sign
• Increased length to the vaginal wall
• Hypertrophy of the papillae of the vaginal
mucosa

17. REPORODUCTIVE SYSTEM cont
UTERUS
• Uterine hypertrophy of the myocytes
–Hypertrophy can cause venous
compression
–Can result in fall in venous return hence
aggravating fall in CO
• Physiologic compensation
–Rise in peripheral resistance to minimize
fall in blood pressure

18. REPORODUCTIVE SYSTEM cont
• Supine hypotensive syndrome
 Occurs if no physiologic compensation pts
are prone to
 Symptoms: nausea, dizziness, syncope
 Can be relieved with position changes
• Uterine blood flow is Increased 100 ml/min to
1200 ml/min

19. Amenorrhoea
• ⇈ Ostrogens and progesterone cause
negative feedback mechanism to the
hypothalamus leading to suppress production
of GnRH and consequently suppression of
production of the FSH/LH from the pituitary
gland.
• Decreased FSH/LH leads to amenorrhoea
REPORODUCTIVE SYSTEM cont

20. URINARY SYSTEM
a. Anatomical changes:
Marked dilatation of calyces, renal pelves,
and ureters
 More prominent on the right
 Partial obstruction of the ureters can
occur at the pelvic brim
 Progesterone produces smooth muscle
relaxation which is thought to cause the
relaxation noted

21. b. Physiologic changes:
GFR and renal plasma flow
 Increases 40 -50% by mid-gestation,
plateaus, then remains unchanged until
term
 Elevated GFR is reflected in the lower
serum levels of creatinine and blood
urea nitrogen
URINARY SYSTEM cont

22. ENDOCRINE SYSTEM
GLUCOSE METABOLISM
• Postprandial hyperglycemia
– To ensure sustained glucose levels for fetus
• Accelerated starvation
– Early switch from glucose to lipids for fuels
• Insulin resistance promotes hyperglycemia
– ↓ peripheral insulin sensitivity and hence ↓ uptake of
glucose. Cause? hPL, insulinase produced by the
placenta, etc

23. 2. CORTISOL
• ACTH levels increase approx. 2 - 3x during
pregnancy.
– This increase is, in part, placental in origin and may be a
local paracrine effect of placental CRH production.
• The stress of labor causes ACTH(Adrenocorticotropic
Hormone) levels to increase rapidly and then decrease
within two days postpartum.
• The stress of labor causes ACTH levels to increase
rapidly and then decrease within two days
postpartum.

24. GASTROINTESTINAL TRACT
Liver
• Liver morphology unchanged
• Lab Tests similar to liver disease
– Alkaline phosphatase doubles
– AST, ALT, albumin and bilirubin are slightly lower
Gallbladder
• Impaired contraction → high residual volumes
• Promotion of stasis
– Stasis associated with increased cholesterol saturation of
pregnancy, supports predisposition of stones
• Intrahepatic cholestasis
• Retained bile salts----pruritus gravidarum

25. Cont. GASTROINTESTINAL TRACT
GI motility decreases
• ⇈progesterone levels relax smooth muscle.
These may lead to:
– Heartburn and belching
• ?caused by delayed gastric emptying and
gastroesophageal reflux due to relaxation of the
lower esophageal sphincter and diaphragmatic
hiatus
• Constipation
– May be caused by enlarged uterus pressing against
the rectum and lower portion of the colon

26. SKIN CHANGES
1. Chloasma or melasma
gravidarum
 More common in dark skin
people
 Fades a few months after
delivery
 Repeated pregnancy can
intensify
 Can occur in normal non-
pregnant women with
harmless hormonal
imbalances or women on
OCPs or depo

27. SKIN CHANGES cont.
2. Melasma gravidarum
• These are hyperpigmentations
• Causes:
–Melanocyte stimulating effect of estrogen
and progesterone
–The placenta produces a melanocyte-
stimulating hormone

28. 3. Striae gravidarum
• Related to Stretching with
pregnancy
.- Deep collagen deposits break
apart
• Also associated with increased
ACTH secretion which affects
connective tissue
• Depressed red streaks on the
skin of fatty areas: Abdomen,
breasts and thighs
• Regress after delivery
• Residual white streaks remain
(striae albicantes)

29. BREAST CHANGES
• Oetrogen and progesterone together
suppress milk production during pregnancy.
• Progesterone is important for fetal growth
and breast development
• Appearance of striae gravidarum