Normal Pregnancy 2

Question 1

Describe the regulation of placental transfer.

Answer 1

• Concentration of substance in maternal plasma and the extent that it’s bound to a plasma carrier protein
• Rate of maternal blood flow through intervillous space
• Area available for exchange across villous trophoblast epithelium
• Mode of transport (e.g. simple diffusion vs active transport)
• Amount of substance metabolized by placenta during transfer
• Area for exchange across fetal intervillous capillaries
• Rate of fetal blood flow through villous capillaries

Question 2

What are the normal fetal shunts?

Answer 2

• High pulmonary vascular resistance because fetal blood does not need to enter pulmonary vasculature in order to be oxygenated
• Normal fetal shunts
  
  • Ductus venosus
  • Foramen ovale
  • Ductus arteriosus

Question 3

What are the circulatory changes at birth?

Answer 3

• Closure of foramen ovale
• Collapse of ductus venosus and umbilical vessels
• Closure of ductus arteriosus
  
  • Alveolar expansion leads to increased alveolar capillary O2
  • Increased O2 induces marked decrease in pulmonary vascular resistance
  • Results in decreased RA pressure and afterload along with increased pulmonary vascular blood flow
  • Backflow of oxygenated blood into ductus arteriosus results in production of prostaglandins → vasoconstriction/closure of ductus

Question 4

What are the respiratory changes of a fetus throughout its development?

Answer 4

• Fetal breathing movements begin between 16-22 weeks gestation
• Anatomical maturation
  
  • Pseudoglandular stage (5-16 weeks)
  • Canalicular stage (16-25 weeks)
  • Terminal sac/alveolar stage (25 weeks through 8 years of life)
    
    • Production of surfactant by type II pneumocytes

Question 5

What are some key developmental timepoints for fetal GI development?

Answer 5

Swallowing begins at 10-12 weeks.

Question 6

What are some important renal developmental timepoints for the fetus?

Answer 6

Fetal kidneys begin to secrete urine early in pregnancy and accounts for majority of amniotic fluid volume after 16 weeks gestation

Question 7

What are some unique features of fetal hemotology?

Answer 7

• Embryonic hemoglobin
  
  • Several different embryonic hemoglobins are made as gestation progresses during early pregnancy
  • Made in yolk sac
• Fetal hemoglobin
  
  • Composed of two alpha and two gamma chains
  • Produced in fetal liver
  • Increased oxygen affinity for oxygen that adult hemoglobin
  • O2 dissociation curve

Question 8

What are some unique features of the fetal endocrine system?

Answer 8

• Thyroid
  
  • Thyroid hormone critical for normal development, especially that of the brain
  • Fetus starts synthesizing thyroid hormone at 10-12 weeks gestation
  • Dependent upon maternal thyroid hormone prior to this time
• Adrenal glands
  
  • Fetal adrenals at term weight as much as adult adrenals because of large fetal zone that involutes rapidly after birth
  • Huge capability for steroid hormone production
  • Precursor is cholesterol (primarily de novo production)
  • Contributes precursors that are converted by placenta to produce high levels of maternal estrogens