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Placental implantation begins
150 hours after ovulation
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Placental development is complete by
10 days after implantation
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The umbilical cord is made up of
2 arteries, 1 vein, surrounded by wharton jelly
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Route of blood flow from mom to fetus
- Maternal blood
- umbilical vein
- fetal liver
- anastomosis
- fetal sinus venosus
- atria/ventricles
- truncus arteriosus
- aortic sac
- aortic arches
- dorsal aorta
- pair of umbilical arteries
- maternal blood
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Rate of fetal BF
500ml/min
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Fetal BF depends on
fetal cardiac activity, BP, R to L shunt, SVR, PVR
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Factors that reduce UBF
- o Umbilical cord compression
- o Maternal hypo/hypertension
- o Aortocaval syndrome
- o VasoC in uterine vessels (predominantly alpha)
- o Hypertonic uterine contractions
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Fetal oxygenation/gas exchange depend on
adquate UBF, adequate maternal oxygenation
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Normal fetal scalp blood gas
pH>7.25, pCO2 <50, pO2 >20 (variable)
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Critical emergency, fetal ABG
pH <7.2, HCO3 <20, BE> -6
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Main determinant of fetal pO2
Maternal uterine VENOUS pO2
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100% maternal FIO2 will increase fetal pO2 by
10mmHg
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Greatest maternal threats:
- Severe hypoxia
- Hypotension
- Acidosis
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Chronic fetal hypoxia secondary to chronically decreased U/P perferusion are d/t:
- Pre-eclampsia
- Maternal HTN
- Maternal diabetes
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Primary fetal response to acute hypoxia:
- Maintain BF and oxygenation to brain, heart, kidneys
- Brief increased HR, THEN vagally stimulated slowed fetal HR to decrease O2 consumption
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Secondary fetal response to acute hypoxia:
fetal oxy-hgb dissociation curve shifts RIGHT
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Fetal asphyxia:
Loss of cerebral autoregulation, ischemic brain, mental retardation
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