GRADED A+ 2025/2026
Fluid acts as a cushion & protects the vessels in the umbilical cord to allow FREE
FLOW of blood.
What is *Amniotic fluid* composed of? - clear
water, proteins, carbs, lipids, electrolytes, fetal cells, lanugo, vernix caseosa
*FETAL URINE & lung secretions*
When there is DECREASED placental perfusion & increasing hypoxia within the fetus
there will be SHUNTING of the fetal blood away from the fetal extremities & non-vital
organs . . . . . . . perfusion of blood will be prioritized to what organs? - *BRAIN*
*HEART*
*ADRENALS*
If fetus is hypoxic and shunting blood to the brain, heart and adrenal -- there will be
what? - *DECREASED RENAL perfusion* which will cause:
---> decreased urine production
---> decreased output
---> *Decreased Amniotic Fluid*
(Amniotic fluid is an indirect indicator of placental perfusion)
*Oligohydramnios* can be an indicator of what? - ---> *FETAL HYPOXEMIA*
Shunting of oxygenated blood flow away from the extremities, kidneys and liver leading
to reduced urine output and decreased amniotic fluid levels.
Remember it can also be from ruptured membranes which has not been identified yet.
Describe fetal circulation starting within the placenta. - Oxygenated blood from the
placenta enters the *umbilical vein* and then travels to the fetus.
*Bypasses liver* by the *DUCTUS VENOSIS* & combines with deoxygenated blood
within the inferior vena cava.
Blood joins deoxygenated blood from the superior vena cava & empties into the *right
atrium*.
Right Atrium pressure > Left Atrium pressure
*Most blood shunted through foramen ovale*, to the left atrium, left ventricle then Aorta.
The blood that goes to right ventricle and pulmonary arteries is shunted through the
Ductus arteriosis to the aorta. (this prevents blood from entering the lumgs & damaging
capillaries).
Deoxygenated blood returns to the placenta via the *UMBILCAL arteries* which
originatedd form the *internal iliac arteries* near the bladder.
,Where do the umbilical arteries originate from? - internal iliac artery
(near the bladder)
fetal circulation - oxygenated, nutrient-rich blood from placenta carried to fetus via
umbilical vein → half enters Ductus venosus (allows blood to bypass the liver) →carried
to inferior vena cava → RA → RV → Ductus arteriosus (conducts some blood from the
pulmonary artery to the aorta [bypassing the lungs/fetal pulmonary circulation]) → aorta.
Other half enters liver/portal vein → RA → Foramen ovale (allows blood to bypass
pulmonary circulation by entering the left atria directly from the right atria since there is
no gas exchange in fetal lung) → LA → LV → aorta. Illustrated here.
Compare concentration of hemoglobin in fetal blood vs. maternal blood. - Fetal blood
has *50% HIGHER concentration of Hgb* allowing fetal blood to carry *20-30% more
oxygen* than maternal blood.
In addition, fetus has a HIGHER cardiac output & HR which results in rapid ciculation.
Fetal conduction system - SA Node
---> Atrial preferential pathways
---> AV Node
---> Bifurcation of the Left & Right Bundle Branches
---> Peripheral Purkinje networks
---> Ventricular myocardium
What is the pacemaker of the heart? - *SA node*
Where does the *Vagus n.* start? - VAGUS n.
starts in the *medulla oblongata* of the brain & terminates in the SA & AV nodes.
Where is the *cardioregulatory center* which controls FHR control (baseline, variability
& other characteristics)? - *MEDULLA OBLONGATA*
--integrates input from the ANS
SA node triggers the atria to fire and AV node triggers the ventricles.
Stimulation of the *vagus fibers* in the SA and AV nodes will cause what? -
*DECREASE* in the *FHR*
--per parasympathetics
Parasympathetic tone INCREASES with gestational age which causes a *natural
decrease in baseline* FHR & *increase in variability*.
What is true of *parasympathetic tone* in relation to gestational age? - Parasympathetic
tone INCREASES with gestational age which causes a *natural decrease in baseline*
FHR & *increase in variability*.
, A 26 wk baby will likely have what differences on EFM in comparison to near term
baby? - --likely will have a *HIGHER baseline* (by at least 10 bpm)
--May NOT have moderate variability
--Accels are 10x10
A *parasympathetic response* can be achieved with what maneuvers during labor
course? - *head compression*
*vaginal exams* (SVEs)
*repeated scalp stimulation*
*forceps*
*vacuum applications*
some centrally-acting medications
Which medication can BLOCK the vagus n. and cause an *INCREASE in fetal heart
rate*? - *ATROPINE*
Parasympathetics to the heart? - Vagus
Sympathetics to the heart? - T1-5 of heart
Superior Cervical Ganglia C2-3
Middle Cervical Ganglia C6 (may be absent)
Inferior Cervical Ganglia C7, First Rib
Stimulatioin of the Sympathetics on the fetal heart will cause what change? -
*INCREASE in FHR* due to the release of *epinephrine & norepinephrine*.
Improves cardiac output (think flight or fight)
Sympathetic stimulation to the fetus can be achieved by what maneuvers? - *LOUD
noises* (vibro-acoustic stimulation)
*Maternal abdominal stimulation*
*Initial scalp stimulation*
*epinephrine*
anxiety/fear/pain
*atropine*
What part of ANS is responsible for *fetal acceleration* on FHTs? - *SYMPATHETIC
nervous system*
What is a medication which blocks sympathetic stimulation to the fetal hear and can
cause drops in the HR? - *PROPANOLOL* (beta-blocker)
*Variability* of fetal heart rate is largely controlled by what part of ANS? -
*Parasympathetic nervous system*
Presence of variability demonstrates and intact pathway through:
*Cerebral cortex --> Midbrain --> Vagus n.* --> Fetal conduction system