Maternal Physiology in Pregnancy
Jennifer McDonald DO
Role of Estrogen in
Pregnancy
• Increases blood flow to uterus by
promoting vasodilation
• Changes the sensitivity of the system
to CO2
• Softens cervix, initiates uterine
activity, maintain labor
• Develops breast tissue in preparation
for breast feeding
Role of Progesterone in
Pregnancy
• Readies the uterus for implantation
• Relaxes smooth muscle to prevent
SAB
• Prevents maternal immunologic
response to fetus
• Relaxes smooth muscle
• Plays role in development of alveoli &
ductal system in the breast
Changes in Size
Increases
from 50 g to
1000 grams !
Volume
changes from
4 mL to over
4000 mL
Uterine blood flow
increases progressively
and reaches
500 mL/minute at term
Cervical & Vaginal Changes
• Cervix becomes hypertrophied, soft
and bluish in color
• Thick secretions fill the endocervical
canal (“mucous plug”)
• “Chadwick’s” sign – bluish color to
cervix/vagina due to increased
vascularity
Ovarian Changes
• Ovulation ceases
• Corpus luteum continues to grow until
7-8 weeks
Corpus luteum secretes:
1. Estrogen
2. Progesterone
3. Relaxin
Blood Volume
• Increases 35-45% by 32 weeks
• Red blood cell mass increases by 33%
The increase in plasma is greater
and faster than RBC resulting in
physiologic anemia
Hb concentrations falls
from 14 gm/dL
To
12 gm/dL.
Purpose of Increase
• Meets increased demands of
uterus & baby
• Protects against supine
hypotension syndrome
• Protects against fluid loss in
labor
White Blood Cells
• Normal 7.0 mm3
• Rises to 10.5-11 mm3
• Can rise as high as 15-16 mm3 in labor
Coagulation Factors
• Fibrinogen doubled
• Factor VIII tripled
• Factor VII and Factor X are doubled
Pregnancy is a hyper-coaguable state
Cardiovascular Changes
• Apex displaced upwards
and to the left
• Heart size increased
12%
Pulse
• 1st trimester resting pulse increases
by 8 beats/min
• By term increased by 15-20 beats
Heart Sounds
• First heart sound becomes louder and
may split
• Intensity of the second sound may
become louder
• Systolic functional murmurs develop
in most due to tricuspid regurgitation
Cardiac Output
CO = HR x Stroke volume
• Increases 40% by 20 weeks
• Mainly due to increases in SV
• Maintained until 4 days post-partum
Blood Pressure
• Systemic blood pressure overall decreased
• Systolic changes little
• Diastolic reduced (5-10 mmHg)
• Venous pressure upper body unchanged
• Venous pressure in the lower body
increased
• Especially affected by position
Supine Hypotension
• Compression of the
inferior vena cava
• Decreased venous
return
• Decreased cardiac
output
• Lowered blood
pressure
Peripheral Vasodilatation
• Increased blood flow to the skin
especially hands & feet lead to a
feeling of warmth
• Increased congestion of nasal mucosa
leading to nasal congestion
• Epistaxis common
Venous Pressure
• Mechanical pressure on the pelvic
veins
• Increased venous return from the
internal iliac veins  increased
pressure in the external iliac veins
• Increased pressure in lower
extremities predisposes women to
edema & varicose veins
Diaphragm
At term
diaphragm can
be elevated up
to 4 cm
Diaphragm
• Mobility reduced
• Respiration becomes mainly thoracic
• Widened subcostal angle increasing
transverse diameter of the chest
Respiratory Physiology
TV  (30-50%)
TLC  (4-5%)
FRC  (20%)
RV  (20%)
ERV  (20%)
IC  (5-10%)
Respiration
• Shortness of breath common perception by
pregnant women
• Slight increase in respiratory rate
• Increased O2 consumption 15-20%
• Increased TV with normal RR increased MV
• As MV increases hyperventiliation of
pregnancy occurs lowering maternal CO2
• Over-breathing due to progesterone
Renal Changes
• Renal blood flow and GFR
increased by as much as 50%
• Increased excretion
• Decreased serum creatinine &
uric acid
Ureters
Dilatation of the ureters and renal
pelvis
Due to …
• Relaxation by progesterone
• Pressure at the pelvic brim especially
on the right
Urinary Frequency
• Pressure on the bladder by the
enlarging uterus
• Congestion of the bladder mucosa
GI Changes
• Gingivitis
• Reduced sensitivity of taste buds
• Pica
• Decreased GI motility due to
progesterone
• Increased propensity toward
gallbladder disease
Nausea & Vomiting
• 70% of pregnancies
• Elevated estrogen, progesterone
• Dramatic elevations in hCG
• Routinely resolves after 12-14 weeks
• Hyperemesis gravidarum
Constipation
• Decreased motility
• Increased water absorption
• Pressure on the sigmoid colon
• More sedentary
• Iron from prenatal vitamins
Appendix
Appendix
displaced
upwards &
laterally later in
pregnancy
Weight Gain
U n d e rw e ig h t
12 .5 -18 k g
(B M I <19 .8 )
(2 8 -4 0 lb s )
A v e r a g e w e ig h t
11.5 -16 k g
(B M I 19 .8 -2 6 .0 )
(2 5 -3 5 lb s )
O v e r w e ig h t
7 -11.5 k g
(B M I > 2 6 )
(15 -2 5 lb s )
BMI= Weight (kg)/height (m2)
Distribution
• 6 kg maternal tissues (breast
enlargement, blood volume, fat
stores)
• 5 kg fetal tissues (baby, placenta,
amniotic fluid)
7 kg Water
3 kg fat
1 kg protein
Maternal Changes
1600
1400
1200
1000
Uterus
800
Mammary Gland
600
Plasma Volume
400
200
0
10 wk
20 wk
30 wk
40 wk
Fetal Tissue Changes
3500
3000
2500
2000
Fetus
1500
Placenta
1000
Amniotic Fluid
500
0
10 wk
20 wk
30 wk
40 wk
Musculoskeletal Changes
• Increased mobility of pelvic joints
Progesterone & Relaxin
• Flattening of feet
• Progressive lordosis
• Round ligament pain
Dermatologic Changes
Linea nigra
Cholasmsa
Stretch Marks
• Mechanical
stretching of and
rupture of elastic
fibers
• Glucocorticoid
influence
Breast Changes
• Due to increased estrogenic state
• Increased size & vascularity
• Mastodynia very common
• Increased pigmentation of areola &
nipple
• Prominence of Montgomery tubercles