Maternal physiology
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Transcript Maternal physiology
Maternal
physiology
Goals
To understand the normal changes associated with pregnancy
Body Water
TBW increases from 6.5L to 8.5L
At term water content of fetus, placenta and AF is 3.5L
BV, PV, RBC, extravascular, intracellular
Pregnancy is a condition of chronic volume overload
Water retention exceeds Na retention-decreased plasma
osmolality (Na dec by 3-4)
To recognize physiologic and pathologic states during pregnancy
Hematology – Blood volume
Increases progressively from 6 to 8 weeks’
gestation
maximum volume at 32 weeks - 45% increase
possibly due to estrogen stimulation of reninangiotensin-aldosterone system
(Inc Prog, NO->Dec SVR->Dec MAP->Inc
Na retention)
Hematology – RBC mass
Red blood cell mass increases by 250450 cc by term
Increased production
Possibly hormonally mediated
Hematology - Iron
Maternal
normal
requirement is 1000mg
pregnant woman needs to absorb
about 3.5 mg/day of iron
the goal of iron supplementation is to
prevent maternal iron deficiency
iron is actively transported to the fetus
Hematologic changes
IMPLICATIONS
The
increase in plasma volume and rbc mass
translates into a 45% increase in circulating
blood volume
may protect from hemodynamic instability
may serve to dissipate fetal heat production
and provide increase renal filtration
physiologic anemia of pregnancy
may
function to decrease blood viscosity
may improve intervillous perfusion?
Hematology
LEUKOCYTES
Peripheral wbc rises progressively during pregnancy
1st ∆ – mean 9500/mm3 (3000-15,000)
2nd and 3rd ∆ – mean 10,500 (6000-16,000)
Labor – may rise to 20-30,000
Rise is due to increase in pmns (demargination)
PLATELETS
Platelets experience a progressive decline but should
remain within normal range
Likely due to increased destruction
Hematology
COAGULATION FACTORS
Increased
levels
Fibrinogen
(Factor I)
Factors VII through X
No
change in prothrombin (Factor II),
Factors V and XII
Decline in platelet count, Factors XI and XIII
Bleeding
time and clotting time are unchanged in
normal pregnancy
Cardiovascular – Cardiac output
Maternal cardiac output increases about 30-50%
during pregnancy (mean 33%)
pregnancy maximum of 6 L/min
CO remains maximal until delivery
Earliest rise in CO is due to increase in SV
As pregnancy progresses
Gradual increase in mat HR (15-20 bpm rise)
SV declines to near non-pregnant levels
increase HR is what maintains the elevated CO
Cardiovascular – Cardiac output
CO is position dependent
Lower when supine
IVC compression by the uterus reduces venous return to
the heart
At 38-40 weeks, there is a 25-30% fall in CO when
turning from the side to the back
Fall in CO is compensated by a rise in peripheral
vascular resistance
supine hypotensive syndrome (1-10% patients)
Cardiovascular – Cardiac output
Distribution of CO
First trimester and non-pregnant state
Uterus receives 2-3%
By term
Uterus receives 17%
Breasts 2%
Reduction of the fraction of CO going to the
splanchnic bed and skeletal muscle
CO to the kidneys, skin, brain and coronary arteries
does not change
Cardiovascular – Arterial BP
BP varies with position
Peripheral vascular resistance falls during pregnancy
Progesterone’s smooth muscle relaxing effect
?heat production by the fetus vasodilatation
The reduction in PVR may lead to a progressive fall in
systemic arterial bp during the first 24 weeks of
pregnancy
Gradual rise after 24 weeks non-pregnant levels by
term
Cardiovascular – Venous system
Venous compliance increases during pregnancy
decrease in flow velocity and stasis
?progesterone effects on smooth muscle
Forearm venous pressure increases by 40-50%
Calf venous pressures are always higher
due to the enlarging uterus
Cardiovascular - LV function
Left ventricular dimensions and volume increase
during pregnancy
most parameters of LVF are the same as in the nonpregnant state
Ejection fraction, rate of internal diameter shortening,
percentage of fractional shortening, and ventricular wall
thickness
Bottom line: preservation of myocardial
function
Signs and Symptoms of Normal Pregnancy
Symptoms
reduced exercise tolerance
dyspnea
Signs
peripheral edema
distended neck veins
point of maximal impulse displaced to the left
Signs and Symptoms of Normal Pregnancy
Auscultation
increased splitting of the first and second heart
sound
S3 gallop
SEM along the left sternal border
Continuous murmurs
Signs and Symptoms of Normal Pregnancy
CXR
straightening of left heart border
heart position more horizontal – may appear as
cardiomegaly on cxr
increased vascular markings in lungs
ECG
left axis deviation
non-specific ST-T wave changes
Cardiovascular - Labor
First stage of labor: 12-31% rise on CO due to
an increase in SV
Second stage of labor: 34% increase in CO
Not only pain-related
UCs result in the transfer of 300-500 cc of blood
from the uterus to the general circulation
Enhanced venous return to the heart
Increase in CO by 10-15%
Cardiovascular - Postpartum
Immediate pp period: 10-20% rise in CO
release of obstruction of venous return
extracellular fluid mobilization
Rise in CO associated with reflex bradycardia
SV increases this may persist for one to two
weeks after delivery
QUESTION
During which of the following states is the
blood pressure lowest?
a)
b)
c)
d)
First trimester
Second trimester
Third trimester
Non pregnant
QUESTION
Increased cardiac output immediately
postpartum is due to:
a)
b)
c)
d)
Increased HR
Release of obstruction of venous return
Reduced mobilization of extracellular fluid
Reduced stroke volume
Respiratory system
UPPER RESPIRATORY TRACT
Hyperemic mucosa of nasopharynx
Estrogen-mediated
nasal stuffiness and epistaxis
Polyposis of nose and sinuses may occur and regress after delivery
“chronic cold”
MECHANICAL CHANGES
Configuration of thoracic cage changes early in pregnancy
Increase in subcostal angle, transverse diameter and circumference of chest
With advancing gestation, the level of diaphragm is pushed up
Changes in pulmonary function tests
during pregnancy
Serial
Serialmeasurements
measurementsofoflung
lungvolume
volumecompartments
compartmentsduring
duringpregnancy.
pregnancy.Functional
Functional
residual
residualcapacity
capacitydecreases
decreasesapproximately
approximately2020percent
percentduring
duringthe
thelatter
latterhalf
halfofof
pregnancy,
pregnancy,due
duetotoa adecrease
decreaseininboth
bothexpiratory
expiratoryreserve
reservevolume
volumeand
andresidual
residualvolume.
volume.
Redrawn
Redrawnfrom
fromProwse,
Prowse,CM,
CM,Gaensler,
Gaensler,EA,
EA,Anesthesiology
Anesthesiology1965;
1965;26:381.
26:381.
Respiratory system
LUNG VOLUME AND PULMONARY
FUNCTION
30-40% increase in tidal volume (Amount of air I
and E with each breath)
30-40% increase in minute ventilation (likely P4 mediated)
ERV falls by 20%
Vital capacity and inspiratory reserve volume remain
unchanged
Respiratory system
GAS EXCHANGE
Minute ventilation rises 30-40% by late pregnancy
O2 consumption increases only 15-29%
Results in higher PAO2 (alveolar) and PaO2 (arterial)
Normal PaO2: 104-108 mmHg
Fall in PACO2 and PaCO2 levels
Normal PaCO2 level: 27-32 mmHg
Increases gradient of CO2 facilitating transfer from fetus to mother
Arterial pH remains unchanged
Increased bicarbonate excretion via kidneys
Respiratory system
DYSPNEA OF PREGNANCY
Common complaint
60-70% of patients
late first or early second trimester
Likely due to various factors
reduced PaCO2 levels
awareness of increased tidal volume of pregnancy
QUESTION
Which of the following is increased in
pregnancy?
a)
b)
c)
d)
FRC
ERV
RV
TV
Renal system
ANATOMY
Kidney enlargement
increased renal vascular and interstitial volume, R>L
Ureteral and renal pelvis dilatation by 8 weeks
Right > left
mechanical compression by uterus and ovarian venous plexus
smooth muscle relaxation by progesterone
Implications
Increased incidence of pyelonephritis
difficulty in interpreting radiographs
interference with studies
Renal system
RENAL HEMODYNAMICS
Effective renal plasma flow (ERPF) and GFR
increase
Filtration fraction falls
Returns to normal by late third Δ
Endogenous creatinine clearance increases
Begins by 5 weeks
Renal system
METABOLITES
increased GFR decline in serum urea and creatinine
BUN – 8-9 mg/dl by end 1st Δ
Decline in serum creatinine
0.7 mg/dl by end 1st Δ
0.5-0.6 mg/dl by term
Early decline in serum uric acid levels
nadir at 24 weeks
same as nonpregnant level at end of pregnancy due to increased
reabsorption of urate
Renal system
SALT AND WATER METABOLISM
Plasma osmolality begins to decline by 2 weeks after
conception
Sodium loss during pregnancy
reduction in serum sodium and other anions
50% rise in GFR
Progesterone: natriuresis
Renal tubular reabsorption of Na+ increases (aldosterone,
estrogen and deoxycorticosterone)
Sodium homeostasis
Renal system
NUTRIENT EXCRETION
Increase in glucose excretion
1-10 g glucose excretion per day
implications
inability to use urine glucose
susceptibility of pregnant women to UTI
Increase in amino acid excretion during gestation
Due to 50% increase in GFR
no increased protein loss (100-300 mg/24 hr)
Increased urinary loss of folate and vitamin B12
QUESTION
All of the following are increased in pregnancy
except:
a)
b)
c)
d)
Renal plasma flow
GFR
Serum creatinine
Tubular sodium resorption
Gastrointestinal - Appetite
Increase early 1st Δ
Increase intake 200 kcal by end 1st Δ
RDA: 300 kcal/day during pregnancy
Sense of taste may be blunted
Pica
check for poor weight gain and refractory anemia
South - clay or starch (laundry or cornstarch)
UK – coal
Also soap, toothpaste and ice pica
Gastrointestinal - Mouth
Unchanged pH or production of saliva
Saliva production is unaltered
Ptyalism – usually in women with HEG
Gums – edematous and soft
due to inability to swallow
Can lose up to 1-2 L of saliva per day
Decreasing starchy foods might help
May bleed after brushing
Epulis gravidarum
regress 1-2 mos after delivery
excise if persistent or excessive bleeding
Gastrointestinal - Stomach
Decreased tone and motility
Conflicting info about delayed gastric emptying
Reduced tone of the gastroesophageal junction
sphincter
progesterone
possibly due to decreased levels of motility
Increased intraabdominal pressure leads to acid reflux
Lower incidence of PUD
may be due to decreased gastric acid secretion
delayed emptying, increase in gastric mucus, and
protection of mucosa by prostaglandins
Gastrointestinal - Small bowel
Reduced
motility of small bowel
increased
transit time in the third
trimester and postpartum
Enhanced
as
iron absorption
a response to increased iron needs
Gastrointestinal - Colon
Constipation
Mechanical obstruction by the uterus
Reduced motility (p4)
Increased water absorption
Portal venous pressure is increased
Dilation of gastroesophageal vessels
issue in those with preexisting esophageal varices
Dilation of hemorrhoidal veins
hemorrhoids
Gastrointestinal - Gallbladder
Fasting and residual volumes double in 2nd and
3rd Δ
Slower rate of emptying
Biliary cholesterol saturation increases and
chenodeoxycholic acid decreases
increased risk gallstone formation
Gastrointestinal - Liver
Liver does not enlarge
Hepatic blood flow remains unchanged
Spider angiomata and palmar erythema
CO to the liver decreases by ~35%
elevated estrogen levels
Lab data
Drop in serum albumin
Rise in serum alkaline phosphatase
placental production and some hepatic production
Rise in serum cholesterol, fibrinogen, ceruloplasmin, binding proteins for
corticosteroids, sex steroids, thyroid hormones, and vitamin D
No change in serum bilirubin, AST, ALT, protime and 5’ nucleotidase
Rise in GGT is controversial
Gastrointestinal system
NAUSEA AND VOMITING
Morning sickness complicates 70% of pregnancies
Onset 4-8 weeks up to 14-16 weeks
Cause?
Relaxation of smooth muscle of stomach, elevated levels of steroids
and hCG
Rx – supportive: reassurance, support, and avoiding triggers…
HEG
weight loss, ketonemia, electrolyte imbalance and dehydration
possible renal or hepatic damage
IVF, antiemetics
NPO
continue IV
Conclusion
Understanding maternal physiology is crucial in
understanding the changes and clinical scenarios
associated in pregnancy
This knowledge will help us distinguish the
physiologic and pathologic processes during
pregnancy
This knowledge will also improve patient’s
education about their pregnancy
Endocrine - Thyroid
The normal pregnant woman is euthyroid
Changes in thyroid morphology and lab indices
Serum TSH decreases early in gestation
role of hCG stimulating the thyroid
Rise in TBG leads to rise in total T4 and total T3
rises to pre-pregnancy levels by end of first Δ
T4 increases early in gestation
Estrogen-induced increase in TBG
Decreased circulating extrathyroidal iodide
Thyroid enlargement usually not detected by exam
Normal thyroidal uptake of iodide
active hormones free T4 and free T3 are unchanged
Free T4 is the most reliable method of evaluating thyroid function in
pregnancy
Endocrine - Adrenal glands
Expansion of the zona fasciculata
Plasma corticosteroid-binding globulin (CBG) rises
increased production and delayed clearance
Plasma DOC (deoxycorticosterone) rises
due to enhanced liver synthesis
Free plasma cortisol rises
site of glucocorticoid production
fetoplacental unit
DHEAS (dehydroepiandrosterone) decreases
Testosterone is slightly elevated
Increased SHBG and androstenedione
Endocrine - Pancreas
Fetus primarily depends on glucose
Facilitated
diffusion
carrier-mediated
process
but not energy dependent
Active transport of amino acids to the
fetus
Ketones diffuse freely across the placenta
Endocrine - Pancreas
Hypertrophy and hyperplasia of the B cells
Fasting associated with accelerated starvation
maternal hypoglycemia, hypoinsulinemia and hyperketonemia
due to diffusion of glucose by the fetoplacental unit
Feeding response
hyperglycemia, hyperinsulinemia, hypertriglyceridemia and
reduced tissue sensitivity to insulin
glucose response greater during pregnancy
peripheral resistance to insulin: diabetogenic effect of pregnancy.
hPL and cortisol mediated
greater insulin resistance as the pregnancy advances
Endocrine - Pituitary
The pituitary gland enlarges in pregnancy
proliferation
of chromophobe cells on the
anterior pituitary
stalk remains midline
Skin
Spider angiomata (face, upper chest, and arm)
and palmar erythema
elevated estrogen levels
both regress after delivery
Striae gravidarum
Increased eccrine sweating and sebum excretion
Skin
Hyperpigmentation
Melasma: “mask of pregnancy”
Nevi may darken, enlarge or show increased activity
rapidly changing nevi should be excised
Hairs in telogen phase decrease in late pregnancy
elevated e2 and p4
increases after delivery
hair loss 2-4 mos pp
re-growth in 6-12 mos
Masculinization of the skin rarely occurs
evaluate for possible luteomas of pregnancy (which regress
after delivery)
Breasts
Early change
tenderness, tingling and heaviness
vascular engorgement leads to enlargement
Ductal growth due to e2
Alveolar hypertrophy due to p4
Enlargement and pigmentation of areolae
Colostrum may be expressed later in pregnancy
Milk production
E2, p4, prolactin, hPL, cortisol and insulin
Lactation likely due to drop in estrogen and progesterone
after delivery
Skeleton
Lordosis
keep center of gravity over the legs
back pain…
Relaxin
relaxation of the pubic symphysis and sacroiliac
joints
facilitates vaginal delivery but may lead to discomfort
Implications
unsteadiness of gait and trauma from falls
Skeleton
Total serum calcium declines throughout pregnancy
until 34-36 weeks
Serum ionized calcium is constant and unchanged
due to the fall in serum albumin
“Physiologic hyperparathyroidism”
increased gut absorption
decreased renal losses
no bone loss seen in bone density studies
preservation due to calcitonin?
Rate of bone turnover and remodeling increases
throughout pregnancy
twice as great at term
Eye
Increased
thickness of cornea due to
fluid retention (contact lens
intolerance)
Decreased
intraocular pressure