Obstetric Physiology Flashcards
What happens to the location of the maternal heart during pregnancy?
it is displaced upward and to the left, assuming a more horizontal position as the apex moves laterally
What happens to the four chambers of the maternal heart during pregnancy?
- there is an increase in ventricular muscle mass
- there is an increase in left atrial and ventricular volume
How does maternal cardiac output change over the course of pregnancy and what parameters account for this change?
- cardiac output increases primarily in the first half of pregnancy, due to an increase in stroke volume
- it further increases in the second half as a result of increased maternal heart rate while stroke volume returns to normal
- late in pregnancy, it often declines as venous return is impeded by vena canal obstruction by the gravid uterus
Describe the timeline for changes in maternal blood volume during pregnancy.
- the volume begins to increase by 6-8 weeks gestation
- it peaks around 32 weeks gestation
What happens to maternal systemic vascular resistance during pregnancy and why?
resistance decreases as the result of…
- progesterone-induced smooth muscle relaxation
- increased production of vasodilatory substances
- arteriovenous shunting to the uteroplacental circulation
When a pregnant individual lays supine, the uterus often compresses and obstructs the vena cava late in pregnancy. How does this affect their cardiovascular status and what happens to the obstructed blood?
- this change reduces venous return and thus cardiac output
- instead, blood is shunted through the dilated paravertebral collateral circulation
The uterus receives how much of the maternal cardiac output at term?
about 20%
What happens to blood pressure during the course of pregnancy?
diastolic pressure decreases beginning around week 7 and reaches a maximal, 10 mmHg, decline between 24-26 weeks before trending upward again
What happens to maternal pulse during the course of pregnancy?
it increases as pregnancy progresses to about 10-18 bpm greater than the non-pregnant value
What maternal cardiovascular changes are seen during pregnancy?
- the heart is shifted up and to the left, laying more horizontal
- ventricular mass and left-sided cardiac volume increase
- diastolic blood pressure declines
- pulse quickens
- blood volume peaks around week 32
- cardiac output increases, first due to stroke volume and then due to changes in pulse
- vascular resistance decreases
- vena caval return is obstructed by the growing uterus when supine
What is inferior vena cava syndrome?
- a syndrome seen in late pregnancy
- caused by a growing uterus which may compress and obstruct the inferior vena cava while supine
- presents with dizziness, light-headedness, and syncope
What changes are expected during auscultation of the maternal heart during pregnancy?
- widened S2 split
- possible S3 gallop
- low-graded systolic ejection murmur
What kinds of auscultation findings are never considered normal during pregnancy?
S4 heart sounds and diastolic murmurs
What anatomic changes are seen in the maternal respiratory system during pregnancy?
- the diaphragm is elevated about 4 cm
- the subcostal angle wides as chest diameter and circumference increase
What functional changes are seen in the maternal respiratory system during pregnancy?
- there is an increase in total body oxygen consumption
- diaphragmatic elevation reduces the residual and functional residual capacity as well as total lung volume
- respiratory rate is unchanged and tidal volume increases
How do maternal respiratory rate and pulse change during pregnancy?
- pulse quickens by 10-18 bpm
- respiratory rate is unchanged
How does maternal minute ventilation change during pregnancy?
- the respiratory rate is unchanged
- the tidal volume increases
- the minute ventilation increases proportionally
How does acid-base status change during pregnancy?
there is a metabolically compensated respiratory alkalosis with no change in overall pH due to…
- an increase in minute ventilation secondary to an increase in tidal volume
- progesterone increasing central chemoreceptor sensitivity to carbon dioxide
How does the material system compensate for the respiratory alkalosis induced by progesterone and expansion of the tidal volume?
there is an increase in renal excretion of bicarbonate
Pregnancy women often experience what respiratory symptoms during pregnancy?
- dyspnea is common
- allergy-like symptoms secondary to mucosal hyperemia, nasal stuffiness, and increased nasal secretions
What hematologic changes are seen during pregnancy?
- increase in plasma volume
- increase in red cell volume
- increase in total blood volume
- increase in total coagulation factors
By how much do we expect plasma volume, red cell volume, and blood volume to change during pregnancy?
- plasma volume increases by 50%
- red cell volume increases to 450 mL
- maternal blood volume increases 35%
Why do we use supplemental iron during pregnancy? How much is required? What happens if there are insufficient levels?
- recommend 27 mg of supplementation each day to achieve the required 60 mg a day in conjunction with diet
- iron is actively transported to the fetus so fetal hemoglobin levels will be unaffected by maternal iron stores
- so supplementation is essential for preventing iron deficiency of the mother as red cell volume expands
What happens to the white count during pregnancy?
there is an increase in granulocytes and therefore white cell count secondary to stress-associated demargination
The amount of which clotting factors increases during pregnancy? Which decrease and which remain unchanged?
- most increase
- FII, FV, and FXII are unchanged
- protein C and S are decreased
What happens to hemoglobin during pregnancy?
- total hemoglobin increases
- hemoglobin concentration decreases due to dilution
What is the threshold for anemia during pregnancy?
when hemoglobin drops below 11 g/dL, this is indicative of iron deficiency and anemia
What anatomic change is observed in the maternal kidney during pregnancy?
- an enlargement and dilation of the kidneys and urinary collecting system
- the kidneys lengthen due to greater interstitial volume and distended vasculature
Why does the right ureter often dilate to a greater degree than the left during pregnancy?
because the uterus classically undergoes dextrorotation as it enlarges, compressing the right ureter to a greater degree
Give two reasons why the ureters dilate during pregnancy?
- compression by the uterus leads to distention and dilation
- progesterone levels promote smooth muscle relaxation
What happens to the total capacity and residual volume of the bladder during pregnancy? Why?
- the uterus compresses the bladder, reducing total capacity
- elevated progesterone levels relax smooth muscle and decrease bladder tone, raising residual volume
What functional changes are seen in the kidneys during pregnancy?
- there is an increase in renal plasma flow and GFR
- as a result urinary glucose excretion increases and excretion of amino acids and water-soluble vitamins also increases
- there is no change in protein excretion
- the increase in filtration of electrolytes is compensated for by an increase in tubule reabsorption so there is no change in electrolyte metabolism in the kidneys
- serum creatinine and BUN decrease as clearance increases
What finding on UA is never normal during pregnancy?
while increased glucose, amino acids, and water-soluble vitamins are commonly found in the urine, an increase in urinary proteins is never normal
What are the clinical implications of bladder changes during pregnancy?
- urinary frequency
- stress incontinence
- urinary stasis predisposing to pyelonephritis
What happens to urinary glucose, sodium, BUN, creatinine, and protein; GFR; and RPF during pregnancy?
- GFR and RPF both increase during pregnancy
- glucose excretion increases
- sodium filtration increases but so does reabsorption so excretion is unchanged
- BUN clearance increases
- creatinine clearance increases
- there should be no change in urinary protein
What part of the GI tract increases in size?
the portal vein; the stomach, intestines, liver, biliary tract, etc. do not change in size
What functional changes are observed in the maternal GI system during pregnancy?
- progesterone produces relaxation of the lower esophageal sphincter, decreased GI motility, and impaired gallbladder contractility
What causes gastroesophageal reflux during pregnancy?
- progesterone-induced relaxation of the lower esophageal sphincter
- increased intragastric pressure relative to intraesophageal pressure
Why are pregnant women more likely to suffer from gallstones?
- progesterone relaxes and thus impairs contraction of the gallbladder, leading to stasis
- estrogen inhibits intraductal transport of bile acids which lower the solubility of bile
During what portion of pregnancy is morning sickness most prevalent?
beginning between weeks 4-8 and ending around weeks 14-16
What is hyperemesis gravidarum?
severe nausea and vomiting of pregnancy which can result in weight loss, ketonemia, and electrolyte imbalance
What is ptyalism?
a perceived excess production of saliva, which is likely to due an inability of nauseated woman to swallow the normal amounts of saliva being produced
What contributes to constipation during pregnancy?
- mechanical obstruction of the colon
- reduced motility within the GI tract
- increased water reabsorption
Intense pruritis during pregnancy may be indicative of what GI dysfunction?
may be indicative of intrahepatic cholestasis and increased serum bile acid concentrations
What changes are seen in the gums during pregnancy?
they become edematous and soft, bleeding easily with brushing
What happens to total albumin and serum albumin during pregnancy?
- total albumin increases
- but there is a dilutional decrease in serum albumin
How does thyroid function change during pregnancy?
although there are many changes in regulation, there is an overall euthyroid state
- the thyroid enlarges without producing thyromegaly or goiter
- B-hCG in the first trimester stimulates T4 secretion and a transient rise in free T4 concentration
- as the pregnancy progresses and B-hCG drops, estrogen induces hepatic synthesis of TBG and an increase in total T4
- the concurrent stimulation causes free T4 and T3 levels to be unchanged
What adrenal changes are observed during pregnancy?
- estrogen drives hepatic synthesis of cortisol-binding globulin and the concentration of free plasma cortisol progressively increases
- corticotropin levels rise in conjunction
- aldosterone levels increase
- estrogen drives renal synthesis of deoxycorticosterone rather than increased adrenal production
Through what mechanism does deoxycorticosterone levels rise during pregnancy?
estrogen drives renal synthesis; there is limited change in adrenal production
What happens to DHEAS levels during pregnancy?
levels decrease due to hepatic uptake and conversion to estrogen
How does carbohydrate metabolism change during pregnancy?
- there is a diabetic effect characterized by insulin, hyperinsulinemia, and hyperglycemia as a result of human placental lactose, which increases insulin resistance in peripheral tissues
- secondarily, there is an increase in hepatic glycogen synthesis and storage and inhibition of gluconeogenesis
Through what transport mechanism does glucose reach the fetus?
facilitated diffusion across the placenta
How does pregnancy affect lipid metabolism?
- there is an increase in circulating lipids, cholesterol, lipoproteins, and apolipoproteins
- early in pregnancy central fat storage predominates and then in later pregnancy, lipolysis predominates
What happens to the spine during pregnancy and why?
there is a state of lumbar lordosis (anterior convexity) which helps keep the woman’s center of gravity over her legs but leads to complaints of low back pain
When does the pubic symphysis relax and separate and under the control of which hormones does this occur?
it occurs between approximately 28-30 weeks gestation under the control of relaxin and progesterone
Describe changes in calcium metabolism during pregnancy.
- maternal serum-ionized calcium is unchanged but maternal total serum calcium decreases
- a rise in parathyroid maintains serum calcium without affecting the skeleton due to protection by calcitonin
- although the rate of bone turnover increases, there is no loss of bone density
What dermatologic changes are expected during pregnancy?
- spider angiomata
- palmar erythema
- striae gravidarum
- hyper pigmentation
- linea alba darkens to become the lineage nigra
- melasma
- growth and increased pigmentation of existing skin nevi
- eccrine sweating and sebum production increase
How does hair growth change during pregnancy?
hair growth is maintained but more follicles are in the anagen, also known as growth phase
What is leukorrhea of pregnancy?
a heavier vaginal discharge resulting from increased vascularity and transudation as well as stimulation of vaginal epithelium
What happens to the uterus during pregnancy?
it grows significantly heavier through hypertrophy of existing myometrial cells
What is the effect of estrogen and progesterone on the breasts during pregnancy?
- estrogen stimulation results in ductal growth
- progesterone stimulation results in alveolar hypertrophy
What is the most common ophthalmic complaint during pregnancy? Why does it occur?
- blurred vision is most common
- caused by increased thickness of the cornea secondary to fluid retention and decreased intraocular pressure
What is the primary metabolic substrate for placental metabolism?
glucose
How do the following cross the placenta:
- amino acids
- free fatty acids
- gases
- glucose
- iron
- amino acids: active transport with higher levels in the fetus than mother
- free fatty acids: very limited transfer with higher levels in mother than fetus
- gases: via facilitated diffusion
- glucose: via facilitated diffusion
- iron: via active transport
Describe the pathway of fetal blood flow.
- oxygenated blood is delivered via the umbilical vein
- it by passes the hepatic circulation as it enters the IVC via the ductus venosus
- from there it is delivered into the right atrium and passes through the foramen ovale into the left atrium
- it fills the left ventricle and is pumped into the ascending aorta to supply the head and body
- deoxygenated blood from the superior vena cava returns to the right atrium and then fills the right ventricle
- it is pumped out of the pulmonary artery but diverted through the ductus arteriosus into the aortic arch
- blood in the aorta, then, is a mix of oxygenated and deoxygenated blood that passes through the body and exits the fetus via the umbilical arteries
What structure does each of the following give rise to:
- ductus arteriosus
- foramen ovale
- ductus venosus
- umbilical vein
- umbilical arteries
- ductus arteriosus: ligamentum arteriosum
- foramen ovale: fossa ovalis
- ductus venosus: ligamentum venosum
- umbilical vein: ligamentum teres
- umbilical arteries: medial umbilical ligaments
What happens to fetal blood that enters the right hepatic vein rather than the ductus venosus?
it enters the inferior vena cava and then flows preferentially through the tricuspid valve to the right ventricle
What are the components of fetal hemoglobin?
two alpha-chains and two gamma-chains
What is the key difference of fetal hemoglobin?
it binds 2,3-DPG with less affinity and thus has higher oxygen affinity and saturation than HbA
What causes a transfer of oxygen from maternal blood to fetal blood at the placenta?
- HbF has a greater affinity for oxygen than HbA
- additionally, the maternal respiratory alkalosis facilitates transfer of CO2 from the fetal circulation to maternal
- this loss of CO2 causes a rise in fetal blood pH, shifting the oxygen dissociation curve to the left, increasing oxygen-binding affinity
- all while the opposite shift occurs in the maternal blood
When during gestation does the gonadal tissue differentiate into testes? What if it differentiates into ovaries instead?
- differentiation into testes occurs at 6 weeks
- otherwise differentiation into ovaries occurs at 7 weeks
