Practical 3 - Placentation and twinning Flashcards
When and why does the placenta start to develop?
The beginning of week 4
- large increase in foetal demand
Major change at week 9
-increased SA to facilitate exchange - villi
From which cell line does the placenta develop
Trophoblast and extraembryonic mesoderm (chorionic plate) = foetal component
Uterine endometrium = maternal components
What is the difference between cytotrophoblast and syncitiotrophoblast
Cytotrophoblast
- inner layer - invades spiral arteries
Syncitiotrophoblast
-epithlial covering of highly vascular embryonic placnetal villi - invade uterus
Outer layer of embryo = cytotrophoblast, syncitiotrophobalst, intermediate mesoderm
What are the layers of amniotic sac
amnion - foetal side
Chorion - outermost foetal mmbr (trophoblast & extraembryonic; mesoderm)
Decidua basalis: maternal side
How many vessels does the umbilical cord contain
2 x Umbilical artery
= supply deoxygenated blood of foetus to placenta
1 x umbilical vein - oxygenated blood - placenta –> embryo
What are the features of the normal full term placenta
MATERNAL SIDE
15-20 cotyledons (spiral arteries drain into these)
- due to septum formation in decidua)
-septa have core of maternal tissue and coating of syncitial cells
-keeps maternal blood in intervillous lakes and separate from foetal villi
FOETAL SIDE
- covered by chorionic plate
- chorionic vessels –> umbilical cord
What are the hormonal functions of the placenta
End of fourth month - sufficient progestrone to support pregnancy
First two months - hCG - maintains corpus luteum - probabaly synthesized in syncitiotrophoblast
Oestrogenic hormones - estriol
Somatotropin
Where does gas exchange occur in the placenta
-
What substances can cross the placenta
O2 CO2 Hormones Amino acids Carbohydrates Free fatty acids Maternal antibodies - IgG
What are the three foetal shunts, when does each close
Foramen ovale
Ductus Venosus
- Shunt from left umbilical vein to IVC
- Bypasses liver
- Closes 3-7 days post-natally
Ductus Arteriosus
-closes approximately 1 day post-natally
What becomes of the umbilical vein
Remains open at birth - closes in first week
Obliterates –> ligamentum venosum
What is the incidence of PDA
8/10,000
Normally, contraction of muscular wall after birth –> ligamentum arteriosus
Why are NSAIDs contraindicated in late pregnancy
Ass. w/ risk of premature closure of FDA and oligohydramnios
- inhibit COX1/2 - rate limiting enzymes for prostaglandins synthesis
What is a hyatidiform mole
Molar pregnancy
- diploid - only paternal chromosomes
- abnormal blastocyst (hypoplasia) - some syncitiotrophobalst only
- blastocyst demise, trophoblast develops
Placental mmbr with little/no embyro
What does the genetics of a molar pregnancy suggest
Paternal genes regulate trophoblast development
Formed by fertilisation of oocyte with no nuleus , duplication of male chromosomes
What are the RF for molar pregnancy, how common is it?
1/1000
previous molar preg
Age < 20, >35
How do you detect a molar pregnancy
USS- snowstorm
Bloods - hCG Raised
What might molar pregnancy progress to
Ectopic choriocarcinoma
What is placenta previa and its RF
Low lying placenta
1/200
>1 child C section Uterine surgery Multiple pregnancy Cocaine Smoking
What are the complications of placenta previa
Haemorrhage
Maternal and foetal death
Preterm
How is placenta detected prenatally and managed
USS
Mx-
- depends on amount of bleeding, if it stops, maternal health, foetal health
- C section
What is placenta accreta, what are the RF
absence of decidua basalis
Placental attachment to myometrium
RF:
- Previous uterine surgery
- Placental position (placenta previa)
What are the consequences of placenta accreta
Post natal haemorrhage
-DIC, ARDS
Prem birth
What is placental abruption, what are the RF
Partial placental detachment from myometrium
1/200
RF:
- Smoking
- Preeclampsia
- Prior abruption
- Trauma
- Cocaine
- Previous section
How does placental abruption present
Acutely
- Sudden onset abdo pain
- Contractions (continuous)
- PV bleed
- Enlarged uterus disproportionate to gestational age
- Decreased foetal movement and HR
How is placental abruption managed
<36 weeks
No signs of foetal or maternal distress
Monitor in hospital
If foetus mature, foetal or maternal distress –> immediate delivery
What is vasa previa and its incidence
1/1200 - 1/5000
Blood vessels unprotectd by placental tissue or umbilical cord
How is vasa previa detected and managed
Vaginal exam
- pulsating foetal vessels in internal os
OR
-Dark PV bleed & foetal compromise
Urgent delivery
-60% mortality if PV bleed - foetal compromise
What is the prognosis for Vasa Previa
If diagnosed antenatally
- 95% survival
If undetected
- likely rupture
What is preeclampsia
HTN & proteinuria in pregnancy
~5%
What are the risk factors of preeclampsia
Pre-existing HTN SLE or Anti-phospholipid syndrome Previous Hx FHx >40yrs d >= 10 yrs between pregnancy BMI >= 35
What are the signs and symptoms of preeclampsia
Symptoms
- headache
- confusion
- Hx Convulsion
- Respiratory symptoms
- Visual disturbances
- N&V
Signs
- RUQ pain
- Decreased urine output
What is HELLP syndrome
Haemolysis
Elevated Liver Enzymes
Low Platelets
Fatigue Headache nausea RUQ PAIN SEIZURES
Associated with preeclampsia/eclampsia
Pathophysiology unknown
- endothelial cell injury
Severe form of preeclampsia
What is the major underlying cause of preeclampsia
Incomplete differentiation of cytotrophoblast cells
- many don’t undergo epithelial to endothelial transformation
Rudimentary invasion of spiral arteries
What is eclampsia and how is it managed
1/2000
Convulsive condition associated with pre-eclampsia
- complication of severe preeclampsia
- new onset of grand mal seizure activity
- typically occurs > 20 weeks gestation
- 80% intrapartum or >48hours post partum
Mx:
- severe preeclampsia -MgSO4 - prevention
- HTN- maintain above 130/90 (placental perfusion)
- seizure - diazepam
What is cord prolapse, how is it managed
Cord protrudes into vagina
Knee to chest position - shift foetus out of pelvis
- globes hand to push foetus upwards
What is monozygotic twinning?
How might the membranes by arranged?
Twins derived from same oocyte
- identical twins
Diamniotic dichorionic
Diamniotic monochorionic
Monoamniotic monochorionic
What is dizygotic twinning?
Fraternal twinning
- 90%
- 2 embryos from 2 separate ova, fertilised by 2 sperm
Which type of twinning is most dangerous
Monozygotic monochorionic monoamniotic
- cord entaglement
Why are the cotyledons inspected
Retained placental tissue
What are complications of multiple pregnancy
TTTS
PRETERM
gestational HTN and diabetes
What types of conjoined twins are most common
Thoracopagus - 20-40%
Omphalopagus - 13-33%
Pyopagus - 18-28%
What is foetal hydrops
Accumulation of fluid in two or more compartments
Jaundice
Haemolytic disease of the newborn
What is haemolytic disease of the newborn
Rhesus +ve infant, rhesus -ve mother
Mixing of blood
Sensitisation of maternal immune system
Anti-D antibodies
Maternal antibodies to foetal RBCs cause lysis of the RBC and anaemia
How is haemolytic disease of the newborn prevented
Screen for Rhesus status and test for Anti-D antibodies to see if mother has been previously sensitised.
Rh -ve women
- Rh immunoglobulins at 28 weeks gestation
What is the oxygen saturation of umbilical vein
80%
What is the oxygen saturation of the umbilical arteries
58%
When does the ductus venosus close
A few minutes post-natally, functional closure
Actual obliteration 2-3 months post-natally
When does the foramen ovale close
Properly fuses about 1 year after birth, although mostly closed immediately
When does the ductus arteriosus close
Almost immediately
-mediated by bradykinin
complete obliteration is thought to take 1-3 months
What is the incidence of patent foramen ovale
25%
What is the most and least common arrangment of mmbr
MOST:
Monochorionic, diamniotic
(Splitting at early blastocyst)
Diamniotic, dichorionic
LEAST:
-monoamniotic, monochorionic
(splitting at bilaminar disc stage)
What are some complciations of twins in utero
Cord entanglement TTS Twin reversed arterial perfusion Abnormal amount of amniotic fluid Vanishing twin Conjoined twin Foetus in fetu
