Implantation 4

Question 1

What happens to the placenta in the third trimester?

Answer 1

Weight will increase from about 300 grams at 28-30 weeks gestation to about 500 grams at term

Question 2

How does the placenta provide adequate nutrition and gas exchange when the fetal mass is effectively outgrowing the placental mass in the third trimester of pregnancy?

Answer 2

• Increased branching of the secondary and tertiary villi into smaller terminal villi at term
  
  • effectively increases surface area of the villi in contact with the maternal blood without having to increase overall placental mass
• Within the terminal villi, fetal capillaries are essentially directly subadjacent to the syncytiotrophoblast layer
  
  • decreases diffusion distance

Question 3

How will the placenta respond if the fetus experiences chronic hypoxia/ischemia in utero prior to term?

Answer 3

• Villi will become smaller sooner
  
  • tries to increase surface area
  • leads to improper growth of the placenta
  • referred to as hypermature villi, distal villous hypoplasia, or Tenney-Parker change
• Local ischemic/hypoxic change in the placenta results in clumping of the syncytiotrophoblast nuclei into “knots”