11/17- Placental Pathophysiology Flashcards
When does fertilization occur? Where?
3-4 days after ovulation
- Occur within Fallopian tube
Describe implantation
- Timeline (start/end)
- Stage that adheres/invades
- Begins 6-8 days post ovulation
- Completed 11-12 days post ovulation
- Blastocyst becomes adherent to and invades into the secretory endometrium
What is the blastocyst?
- Cell layers and differentiation
- Forms from the multicell morula at 4 days post ovulation
- Outer cell layer becomes the placental disc, chorion and villi
- Inner cell layer becomes amnion, umbilical cord and embryo
When does hCG become measurable?
8-10 days after fertilization (in serum)
What is the function of the placenta?
- Transport O2 and nutrients to and remove CO2 and waste from the fetus
- Physical barrier to transport to certain substances, drugs and infectious agents
- Immunologic barrier that prevents cell trafficking between mother and baby
Describe maternal and fetal blood flow and villous permeability of the placenta
Maternal blood flow
- Implantation, spiral arteries, blood pressure, hemoglobin
Fetal blood flow
- Placental size, fetal blood vessels: umbilical cord to villous capillaries
Villous permeability
- Maturation, basement membrane, stromal cellularity, edema, intervillous space
What is decidua? Function?
Decidua is endometrium that has been hormonally influenced by pregnancy
- Acts as a physical and immunologic barrier between placental (fetus) and uterine (maternal) tissues
- Nitabuch’s fibrinoid between decidua and villi
What is seen here?
Nitabuch’s fibrinoid: between decidua and villi
Describe ectopic pregnancy
- Prevalence
- Most common location
- Presentation and timeline
- 1/150 pregnancies
- 90% in the fallopian tubes
- Presentation typ ~6 weeks after last missed menstrual period
- Rupture of tube and intraabdominal hemorrhage may be life-threatening
- Rarely extruded from fallopian tube intact to become an intraabdominal pregnancy
What is seen here?
Tubal pregnancy
What are consequences of intraabdominal pregnancy?
- Fetal compression
- Lithopedion
What is placenta previa?
Abnormally low implantation completely covering cervix
- Baby cannot be born vaginally; would have to go through placenta
What is the presentation of placenta previa?
- Antenatal, painless vaginal bleeding
Describe abnormally “deep” implantation
- Prevents what
- Occurs where
- Abnormal implantation prevents spontaneous separation of the placenta
- Occurs in areas of deficient or absent decidua (endometrium)
- Lower uterine segment or cervix
- Cornu of uterus where fallopian tubes insert
- Overlying scars, (previous c-section, myomectomy)
- Leiomyoma
What is placentra creta describing? Classes?
How much all/part of the placenta attaches abnormally to the myometrium
- Accreta: onto myometrium
- Increta: into myometrium
- Percreta: through myometrium
What is seen here?
- Accreta: onto myometrium
- Increta: into myometrium
- Percreta: through myometrium
Describe uterine rupture
- Prevalence
- __% occur after ____
- Mgmt/treatment
- Location
- Mortality risk
- 1/800-3,000 deliveries
- 20% occur after prior c-section
- 1/17,000-20,000 unscarred uterus
- Many need post partum hysterectomy to control bleeding
- >90% occur in lower uterine segment and frequently involves the cervix
- 50% perinatal mortality
- 4% maternal mortality
Describe the hemochorial placenta
What is seen here?
Basal plate of placenta with maternal vessels (at implantation site)
- 100 arteries and 50-200 veins
Describe the maternal intervillous space
- Timeline
- Blood volume
- Maternal arteries and veins directly enter the intervillous space after 8 weeks gestation
- The intervillous space will contain 400-500 ml of maternal blood in vivo
What becomes the umbilical cord? When?
The body stalk becomes the umbilical cord by the 7th post menstrual week
What are complications of short/long umbilical cords?
- Short cords (under 30-35 cm) are problematic at delivery; may reflect poor fetal movement
- Long cords (>70-100 cm) may cause increased cord accidents (be compressed, cause strangulation…)
Describe umbilical cord insertion issues
- If inserts at periphery, it’s more prone to compression (markedly eccentric cords)
- Velamentous: cord has vessels unprotected by placental disc; easily ruptured (baby will bleed out)
What is Velamentous insertion
- Incidence
- Risks
- Incidence 0.5-1% of deliveries
- Increased risk for thrombosis or rupture of the unprotected vessels
- Ruptured vessel can result in fetal exsanguination in 3 minutes
Describe umbilical cord spiraling
- Benefits
- Degree/direction
- Problems causing increased/decreased spiraling
- Coiling prevents kinking
- 7:1 left (counter-clock-wise)
- Absent or decreased spiraling
- Single umbilical artery, fetal growth problems, aneuploidy, diabetes
- Increased spiraling
- Diabetes, preeclampsia, growth restriction, torsion, stricture, intrauterine fetal demise
Describe the umbilical vessels (typically)
- Number
- Associations
- Normally have two arteries and one vein
- Single artery occurs in 1% of all deliveries
- 20% associated with malformations
- Risk for poor fetal growth and may have intolerance of labor
What is seen here?
Umbilical cord (with vessels)- single artery?
Describe the umbilical vessels themselves
- Large muscular arteries
- Thin walled vein with internal elastic lamina
- No vasa vasorum
- No peripheral nerves
What are chorionic plate vessels? Describe them
- Each umbilical artery produces 8+ branches
- Arteries always cross over veins on placental surface
What is seen here?
Villi
What are the derivatives of the trophoblast? Cells within each?
Cytotrophoblast
- Progenitor cell
Syncytiotrophoblast
- Terminal cell, acts as both epithelium and endothelium
What is the intermediate or invasive trophoblast?
- What does it invade
- Implantation site
- Invades through the decidualized endometrium
- Invades into the inner 1/3rd of myometrium
- Invades into and through the maternal spiral arteries and adapts the vessels for pregnancy
Describe the fetal:placenta weight ratio
Fetus should be 7-8x placenta (?)
Describe villous maturation
What is seen in fetal membranes in 1st vs. 3rd trimester in regard to villi/membranes?
1st TM
- Villi just on implantation side
3rd TM
- Should not see any villi in membranes
Describe the layers of amnion and chorion and the role of the maternal decidua
- Amnion has 5 distinct layers, but is only 0.02-0.5 mm thick
- Chorion has 4 layers and measures 0.1-1.5 mm thick
- Maternal decidua interfaces with free membranes
What is the greatest risk to multiple gestations?
Prematurity
Which have more problems: dizygotic or monozygotic twins?
Monozygotic
Describe the placenta situation with twins
- Two ova will produce two separate placentas; although they may be so close together and fused as to look like one
- Single ovum will produce a variety of twin placentas depending upon when the blastocyst divides
- The later the division the more one-like the placentas
What are the types of placenta situations with twins?
- Dizygotic twins are dichorionic and diamniotic (72%)
- Monozygotic twins may be:
- Dichorionic and diamniotic (8%)
- Monochorionic and diamniotic or monoamniotic (20%)
What is seen here?
Dichorionic diamniotic setup
What is seen here?
Monochorionic diamniotic setup
What is twin-transfusion syndrome?
- Unequal blood flow between monochorionic twins (7-30%)
- Donor twin shunts blood away, results in anemia growth restriction, oligohydramnios
- Recipient twin gets too much blood, results in polycythemia and cardiac overload, polyhydramnios
What is seen here?
Monochorionic monoamniotic setup
Conjoined twins happen when?
Blastocyst divides after 13 days
Describe pregnancy induced HTN (preeclampsia-eclampsia)
- Incidence
- More common when
- Symptoms
- Etiology
- 6% of pregnancies
- More common in first pregnancy
- More common in early and later reproductive years
Sx: hypertension and proteinuria (with or without edema)
Etiology: not completely understood
- Genetics, inflammatory cytokines
- Placental abnormalities
What is something that may occur involving abnormal maternal vessels with preeclampsia/eclampsia?
- Failure of conversion of maternal spiral arteries from a low volume-high resistance system to a high volume-low resistance system
- Atheroma classic pathologic change
What placnetal changes occur in preeclampsia?
- Small placenta
- Infarcts: multiple, large and different ages
- Accelerated villus maturation and exaggerated syncytial knots
What is seen here?
Accelerated villus maturation and exaggerated syncytial knots
What is abruptio placenta (diagnosis)?
(Premature detachment/rupture of placenta?)
Clinical diagnosis with 2+ of the following:
- Antepartum hemorrhage after 20 wks (vaginal bleeding or concealed)
- Retroplacental hematoma (detaching placenta)
- Uterine pain or tenderness (no relaxation between contractions)
- Fetal distress or death
What is seen here?
Abruptio placenta
Describe gestational diabetes
- Incidence
- Risk factors
- Screening when
- Increased risk of what
- 3-10% of pregnancies
- Risk factors: excessive maternal weight gain, obesity, family history, advanced maternal age
- Screening 24-28 weeks
- Increased risk for development of insulin dependent diabetes later in life
Describe the pathogenesis and consequences of gestational diabetes
Maternal hyperglycemia results in large amount of glucose that crosses placenta
- Fetal overgrowth, macrosomia
- Cardiomyopathy
Fetus produces too much insulin
- Hypoglycemia at birth once maternal source of glucose is gone
- Increased risk for respiratory distress
What is seen here?
Features of placenta associated with diabetes
- Huge placenta (top left)
- Villi look completely different (top right)
- Bigger, really round; many vessels within stroma
- Look more immature (vs. preeclampsia/HTN condition that has accelerated maturation)
- Increased risk of thrombosis (bottom right)
What is seen here?
Infant of diabetic mother
- Pancreatic changes (large islets?) (top)
- Cardiac hypertrophy (bottom)
Infant of diabetic mother has what features/risks?
- Risk of morbidity and mortality increases with poor glucose control, higher in insulin dependent diabetics
- Trauma at delivery, shoulder dystocia
- Increased c-section
- Increased in utero fetal demise after 36 week
- Increased congenital malformations
- Increased hemoglobin, hyperbilirubinemia and thromboses
