T2 L17 Placenta and IUGR Flashcards
Describe what happens after fertilisation
Sperm and ovum meet in Fallopian tube 12-24 hours after ovulation
Fusion occurs and 2nd meiotic division occurs
Acrosome reaction makes ovum impermeable to other sperm
Enters uterine cavity at 8 cell stage
What are the steps from a zygote to a blastocyst?
Zygote 2 cell stage 4 cell stage 8 cell stage Morula Blastocyst
How long does it take to form a morula?
72 hours
How long does it take to form a blastocyst?
4 days
What happens during days 4-5?
1) Morula develops a cavity to form a blastocyst
2) Blastocyst thins out to form trophoblast (start of placenta)
3) Rest of cells are pushed up to form inner cell mass (creates embryonic pole)
4) Blastocyst has now reached uterine lumen and is ready for implantation
What happens during days 6-7?
Bilaminar disc of embryo
Inner cell mass differentiates into epiblast and hypoblast layer. 2 layers are in contact
- hypoblast forms extra embryonic membrane and primary yolk sac
- epiblast forms embryo
Amniotic cavity develops within epiblast mass
What happens on day 16+?
Bilaminar disc develops further by forming 3 distinct layers (gastrulation)
- initiated by primitive streak
- epiblast becomes ectoderm
- hypoblast is replaced by cells from epiblast to become endoderm
- epiblast gives rise to mesoderm
What gives rise to the germ layers?
Epiblast
Describe the development of the placenta
Syncytiotrophoblast burrows into myometrium of uterus to invade spiral arteries and start formation of primary, secondary and tertiary villi
Syncytiotrophoblast invades decidua
Cytotrophoblast cells erode maternal spiral arteries and veins
Lacunae between them fill up with maternal blood
Mesoderm develops into foetal vessels
Describe cytotrophoblast cells
Undifferentiated stem cells
Invade maternal blood vessels and destroy epithelium
Give rise to syncytiotrophoblast cells
Reduce in number as pregnancy advances
Describe syncytiotrophoblast cells
Fully differentiated cells
Direct contact with maternal blood
Produce placental hormones
Give examples of hormones produced by the placenta
HCG
HPL
What does HCG do?
Maintenance of corpus luteum during pregnancy
Production of progesterone and oestrogen
What does HPL do?
Growth, lactation
Carbohydrate and lipid
Describe the placental barrier
Maternal blood in lacunae are in direct contact with syncytiotrophoblasts
Mono layer of syncytiotrophoblast / cyntotrophoblast / foetal capillary epithelium is all that separates foetal and maternal blood
Cytotrophoblasts decrease as pregnancy advances
Barrier thins as pregnancy advances to increase SA for exchange
What molecules are transferred across the placenta?
Gases - O2 and CO2 Water and electrolytes Steroid hormones Proteins (poor transport by pinocytosis) Transfer of maternal antibodies
When are maternal antibodies transferred?
After 12 weeks
Mainly after 34 weeks hence the lack of protection for premature infants
What is decidua capsularis?
Endometrium overlying embryo and chorionic cavity
What is decidua parietalis?
Endometrium overlying side of uterus not accompanied by embryo
What is vasa praevia?
Fetal blood vessels cross or run near the internal os
What is the management of vasa praevia?
Deliver by Caesarean section once foetus is above 34 weeks
Where can the placenta be positioned?
Fundal (most common)
Anterior or posterior
Low lying or placenta praevia
What are the consequences of placenta praevia?
Massive bleeding in pregnancy
Painless bleeding
Foetal death
Maternal death
What are the consequences of trophoblastic invasion failure?
Poor maternal foetal mixing of blood
Lack of oxygen and nutrients to the foetus
Foetal growth restriction
Pre-eclampsia
What is placenta accreta?
Placenta has invaded too deep into myometrium and is unable to separate at birth
What are the consequences of placenta accreta?
Uterus can’t contract down
Massive bleeding
What is the treatment for placenta accreta?
Hysterectomy
What is placenta abruption?
Separation of placenta during pregnancy leading to disruption of blood to foetus
What are the consequences of placenta abruption?
Foetal distress Massive bleeding in pregnancy Extremely painful Foetal death Maternal death
When does cleavage of the placenta occur to get dichorionic / diamniotic twins?
Days 1-3
If cleavage of placenta occurs at day 4-8, what is the result?
Monochorionic / diamniotic twins
When does cleavage of placenta occur to get monochorionic / mono amniotic twins?
Days 8-13
What happens if placenta is cleaved at day 13-25?
Conjoined twins
What is SGA?
Small for gestational age
<5th centile
Normal variant or growth restricted
What is IUGR?
<5th centile
Growth restricted - failure to achieve growth potential
What happens in foetal growth restriction?
Deficient placental invasion leads to reduced placental reserve
Foetal need exceeds the supply leading to IUGR
Hypoxia
Foetal vascular redistribution
Oliguria
Abnormal CTG
Foetal death
How is IUGR diagnosed?
Clinical measurement of uterine size
Ultrasound scan
How is uterine size measured?
Symphysis to fundal height
SFH = weeks +/- cms
What is symmetrical foetal growth restriction?
Head circumference and abdominal circumference are all reduced
What are the causes of symmetrical foetal growth restriction?
Chromosomal anomaly
Viral infection
Severe placental insufficiency
Normal small baby
What is asymmetrical foetal growth restriction?
Only abdominal circumference is reduced
What does abdominal circumference reflect?
Size of the liver
Causes of asymmetrical foetal growth restriction?
Placental insufficiency - no excess glycogen is being deposited in the liver
What are the consequences of hypoxia in the foetus?
Blood flow is redirected away from areas of lesser importance to areas of greater importance
What are the ultrasound findings in IUGR?
Small abdominal circumference
Decreased amniotic fluid
Increased blood flow to the brain
Why does hypoxia cause decreased amniotic fluid?
Kidneys produce amniotic fluid
Hypoxia causes blood flow to be redirected away from kidney
What are the clinical features of IUGR?
SFH is smaller than expected
Reduced movements to conserve energy
Foetal heart range changes as hypoxia develops
Foetal death
Why should you wait to deliver in IUGR?
Low chance of survival outside body
Need to give steroids
Reduce need for caesarean
When should you deliver in IUGR?
Once above 32 weeks
If there is doppler abnormality
If there are decreased movements
If CTG is abnormal
What does betamethasone do?
Give to mother, crosses placenta and stimulates alveoli cells to produce surfactant gene
Prevents respiratory distress syndrome
What does surfactant do?
Coats alveoli cells to reduce surface tension and stop collapse of alveoli cells
When is surfactant normally produced?
Between 24 and 34 weeks
Baby usually has enough by 34 weeks for a term delivery
