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
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