210. Anatomy/Physiology of Implantation, Placentation

Question 1

What are the 3 compartments of the placenta?

What are the three parts of each of those compartments?

Answer 1

1. Membranes: Amnion (fetal epithelial), Chorion (fetal mesodermal), Parietal Decidua (maternal modified endometrial)
2. Umbilical Cord: 1 umbilical vein, 2 umbilical arteries, cushioned by Wharton’s Jelly
3. Placental Disc
   Fetal Part: Chorionic Plate (fetal surface, with arborizing fetal vessels), Villous Tree (fetal vessels surrounded by trophoblasts)
   Maternal Part: Basal Plate (maternal Surface, with decidua, remodeled vessels w/o muscle supplying blood to intervillous space, extravillous trophoblasts (fetal), fibrinoid (fetal)), intervillous space (maternal blood)

Question 2

What is the villous tree and what are the 2 main cell types?

Answer 2

Chorionic Villi: embryo derived structure containing fetal blood vessels and surrounded by trophoblasts

Syncytiotrophoblast: outer layer, main cells of placenta, multinucleated (syncytium), permeable to oxygen/nutrients but NOT blood (no mixing)

Cytotrophoblast: inner layer stem cells (replenish syncytiotrophoblasts), continuous or discontinuous in chorionic villi

Question 3

Define the following abnormalities of implantation

• Ectopic Pregnancy
• Placenta Previa
• 3 types of invasive implantation

Answer 3

EP: implantation outside uterus, usually fallopian tube, high risk of rupture/hemorrhage

PP: low implantation over cervical os, placenta blocks vaginal delivery (risks: maternal hemorrhage, fetal hypoxia), tx: C section

1. Placenta accreta: implants on myometrium
2. Placenta increta: invades into myometrium (needs C section)
3. Placenta percreta: invades through uterine serosa to adjacent structures

Question 4

What is Maternal Vascular Malperfusion (MVM)?

• CP
• mechanism

Answer 4

Pathologic changes assoc with uteroplacental insufficiency (inadequate O2 delivery from mother to placenta)
CP: HTN, preeclampsia
Mechanism: normally maternal vessels remodeled by trophoblasts (low R, high flow); in MVM, maternal vessels retain muscular wall = chronic placental hypoxia = increased villous branching and higher risk of vessel injury (fibrinoid necrosis, foamy macrophages)

Question 5

What is Fetal Vascular Malperfusion? What is it caused by?

What are different types of umbilical cord abnormalities? What are the consquences?

Answer 5

FVM: pathologic changes assoc w/ fetoplacental insufficiency due to processes obstructing/compromising blood flow from fetus to placenta

Abnormal cord insertion

• Velamentous insertion: cord into membrane = risk of kinks/injury - no protection from Wharton’s jelly
• Twisting: hyper-coiled cords forming strictures/compromising blood flow

Mechanical Obstruction:

• knots
• entrapment (nuchal cord, body cord) - life-threatening
• can lead to thrombus formation (stasis, vascular damage)

Path: avascular villi, thrombosed vessel, apoptosed vetal vessels (no internal capillary on villi)

Consequences: High grade FVM = neuro damage (cerebral palsy)
Severe = intrauterine/neonatal demise

Question 6

Twins

• MZ vs DZ
• chorionicity
• amnionicity
• 3 complications of twin pregnancy

Answer 6

DZ: fraternal, 2 eggs, 2 sperm, dichorionic, diamniotic, most commonly due to assisted reproduction

MZ: identical, 1 egg, 1 sperm, shares placenta
Division Early (di-to-mono-chorionic, diamniotic), Late (monochorionic, monoamniotic)

C: Dichorionic: most twins, dividing membrane thick, opaque, firmly adhered to disk due to intervening chorion
Monochorionic: almost always MZ twins, dividing membrane thin, translucent, not adhered (90% have intertwin vascular connections)

A: Diamniotic - always with dichorionic, some monochorionic
Monoamniotic: only some monochorionic, conjoined twins rare but may occur

1. Twin-Twin Transfusion Syndrome: donor twin anemic/small, recipient twin plethoric/large
2. Twin Reversed Arterial Perfusion (TRAP): pump twin = hydrops/larger, Acardiac twin = small
3. Cord Entanglement in monochorionic monoamniotic twins

Question 7

What is Gestational Trophoblastic Disease? What are the two types?

Answer 7

GTD: proliferative placental tissue tumors from trophoblasts - produce beta-HCG

1. Molar Pregnancy: overrepresentation of paternal Ch (makes placenta)
   Complete: two sperm fertilize egg w/o maternal DNA or 1 sperm with empty egg that duplicates = 100% Paternal DNA
   - Path: grape-like swollen villi, diffuse trophoblast hyperplasia
   - elevated hCG, no embryo
   Partial: egg has own DNA - 69XXX/69XXY zygote is 67% paternal
   - Path: only some villi edematous, focal trophoblast hyperplasia, embryo abnormal/rarely viable
   - less elevated hCG
2. Choriocarcinoma: pure trophoblast differentiation with NO chorionic villi, highly malignant, rapidly invasive, widely metastasizing (lungs, brain, liver)
   - responds well to chemo
   - Gross: Large hemorrhagic tumor
   - Path: clusters of trophoblasts surrounded by poorly differentiated syncytiotrophoblasts
   - molar pregnancies increase risk of this