T2 L17 Placenta & Intra-Uterine Growth Restriction, Abnormal Fetal Development Flashcards
What is the embryo called 72 hours after fertilisation has occurred?
A morula
How many days after fertilisation does the blastocyst appear?
4 days
What happens to the embryo between days 4 - 5?
The morula develops a cavity and becomes known as a blastocyst.
Blastocyst thins out and becomes the trophoblast –start of the placenta
The rest of the cells move (are pushed up) to form the inner cell mass. This creates an embryonic pole.
The blastocyst has now reached the uterine lumen and is ready for implantation
What happens to the embryo between days 6 - 7?
Inner cell mass differentiates into two layers: epiblast and hypoblast.
These two layers are in contact.
Hypoblast forms extraembryonic membranes and the primary yolk sac
Epiblast forms embryo
Amniotic cavity develops within the epiblast mass
What happens to the embryo at day 16+?
Bilaminar disc develops further by forming 3 distinct layers (this process is known as gastrulation
Initiated by primitive streak.
The epiblast becomes known as ectoderm
The hypoblast is replaced by cells from the epiblast and becomes endoderm
The epiblast gives rise to the third layer the mesoderm.
Which layer gives rise to all the germ layers in the embryo?
The epiblast
Name the germ layers present in the embryo
Ectoderm
Mesoderm
Endoderm
How is the placenta formed?
Syncytiotrophoblast invades decidua (endometrium)
Cytotrophoblast cells erodes maternal spiral arteries and veins
Spaces (lacunae) between them, fill up with maternal blood
Followed by mesoderm that develops into fetal vessels
What is the function of the foetal vessels?
They aid the transfer of nutrients, O2, across a simple cellular barrier
What happens in pre-eclampsia?
There is an abnormality of invasion by the (syncytiotrophoblast and the cytotrophoblast)
What are the cytotrophoblast cells (CTB)?
Undifferentiated stem cells
Invade the maternal blood vessels and destroy the epithelium
Give rise to the syncytiotrophoblast cells (STB)
What are the syncytiotrophoblast cells (STB)?
Fully differentiated cells
Direct contact with maternal blood (in the lacunae)
Produce placental hormones
What happens to the cytotrophoblast cells (CTB) as pregnancy advances?
They reduce in number
Is the placenta an endocrine organ?
YES
Name two hormones secreted by the placenta and their function
Human chorionic gonadotrophin (HCG)
-maintenance of corpus luteum of pregnancy which releases progesterone and oestrogen
Human placental lactogen (HPL)
- growth, lactation
- increases carbohydrate available for the foetus by increasing the use of lipolysis as an energy source in the mother
What forms the placental barrier?
Mono layer of syncytiotrophoblast/cytotrophoblast/fetal capillary epithelium is all that separates the fetal and maternal blood
What happens to the cytotrophoblasts as the pregnancy advances? Why?
They decrease as they are no longer needed
What happens to the placental barrier as pregnancy advances? What does this result in?
The barrier thins leading to a greater surface area for exchange (over 10m2 )
What structures/molecules are transferred across the placenta?
Gases – oxygen and carbon dioxide (by simple diffusion)
Water and electrolytes
Steroid hormones
Proteins poor – only by pinocytosis
Transfer of maternal antibodies IgG -starts at 12 weeks – mainly after 34 weeks therefore lack of protection for premature infants
Give the topographical name for different parts of the decidua (mucousal layer of the endometrium)
capsularis – overlying embryo and chorionic cavity
parietalis – side uterus not occupied by embryo
basalis – between uterine wall and chorionic villae
What is placenta (or vasa) praevia?
Velomentous cord insertion that runs across the cervical os
The umbilical cord inserts into the fetal membranes (choriamniotic membranes), then travels within the membranes to the placenta (between the amnion and the chorion).
The exposed vessels are not protected by Wharton’s jelly and hence are vulnerable to rupture
What are the different positions the placenta can take in the uterus?
Mainly fundal (at the top)
Anterior or posterior (front wall or back wall)
“low lying” or placenta praevia (near to the cervical os)
What occurs during placenta praevia?
Massive bleeding in pregnancy
Painless bleeding
Fetal death
Maternal death
What happens to the trophoblastic invasion in placenta praevia? What does this result in?
Failure of trophoblastic invasion into maternal circulation at 12 and 18 weeks
LEADS TO:
- Poor maternal fetal mixing of blood
- Lack of oxygen and nutrients to the fetus
- Leads to Fetal Growth Restriction
- Pre-eclampsia (raised Blood Pressure)
What is placenta accreta?
The placenta inserts too deeply into the muscles of the uterus (placenta increta) or grow through the uterine wall (placenta percreta)
It is unable to separate at birth
What complications can placenta accreta lead to?
HEAVY VAGINAL BLEEDING - can cause a life-threatening condition that prevents maternal blood from clotting normally (disseminated intravascular coagulopathy), as well as lung failure (adult respiratory distress syndrome) and kidney failure. A blood transfusion will likely be necessary.
PREMATURE BIRTH - if placenta accreta causes bleeding during pregnancy, there may be need to deliver the baby early.
How is placenta accretia treated?
Hysterectomy
What is placental abruption?
Occurs when the placenta separates early from the uterus (separates before childbirth)
What are the complication of placental abruption?
Massive bleeding in pregnancy (often concealed)
Extremely painful
Fetal death
Maternal death
Give definitions for these 2 types of growth problems
- Small for gestational age (SGA)
- Intra-uterine growth restriction (IUGR)
Small for gestational age (SGA)
- <5th centile
- normal variant or growth restricted
Intra-uterine growth restriction (IUGR)
- <5th centile
- growth restricted (i.e. failure to achieve growth potential)
List the factors that are indicative of foetal growth restrictions
- Deficient placental invasion
- Reduced placental reserve
- Fetal need exceeds supply
- IUGR
- Hypoxia
- Fetal vascular redistribution
- Oliguria
- Abnormal CTG
- Fetal death
How is foetal growth restriction clinically diagnosed?
Clinical suspicion – abdomen “looks smaller”
Clinical measurement of uterine size: Symphysis - fundal height (SFH)
How is the symphysis - fundal height (SFH) measured?
Measured in cm
From the pubic symphysis to the top most portion of the uterus
What is the SFH used for?
Assessment of foetal growth
What occurs in Symmetrical Growth Restriction?
BOTH head and abdominal growth affected
What are the causes of Symmetrical Growth Restriction?
- Chromosomal anomaly (T21)
- Viral infection (Rubella, CMV)
- Severe Placental insufficiency
OR normal small baby (look at the parents)
NOTE: Their head is often proportionate with the rest of their body
What occurs in Asymmetrical Growth Restriction?
ONLY the abdominal circumference is reduced. Abdominal circumference reflects the size of the fetal liver
NOTE: Their head often looks disproportionate to their body
What is the cause of Asymmetrical Growth Restriction?
Placental insufficiency – no excess glycogen being deposited within the liver
What are the consequences of hypoxia in the foetus?
Blood flow (oxygen and nutrients) redirected to areas of greater importance e.g. the brain
Blood flow (oxygen and nutrients) redirected away from areas of lesser importance (organs that the foetus does not actively use) e.g
- the gut (doesn’t eat!)
- the kidneys (placenta clears waste products)
- the lungs (placenta brings O2)
Describe the ultrasound findings in IUGR
- Small AC ( small liver)
- Decreased amniotic fluid ( this is produced by the kidneys)
- Increased blood flow to the brain (look at Middle Cerebral arteries in the brain – using the doppler effect scan
What are the clinical features of IUGR?
- SFH smaller than expected
- Baby’s movements lessen to conserve energy
- Fetal heart rate changes as hypoxia develops (as seen on CTG)
- Fetal death
When and why should you wait/observe if the foetus shows signs of IUGR?
Low chance of survival (outside the womb)
To give steroids
Reduce need for C/S (Caesarean Section)
When should the foetus be delivered if it shows signs of IUGR?
> 32 weeks
Doppler abnormality
Decreased movements
CTG abnormality
What happens when betamethasone/dexamethasone is given to the mother?
The drug crosses the placenta and stimulates the aveoli cells to produce surfactant gene
What is the effect on surfactant the foetal lung?
Stops the collapse of the aveoli cells by coating the cells and reducing the surface tension
Helps prevent Respiratory Distress Syndrome which leads to neonatal death in premature babies
When is surfactant produced in the foetus?
Produced from 24- 34 weeks
The baby will have enough by 34 weeks in preparation for a term delivery
Do premature babies have surfactant?
NO
It is lacking
What happens to the middle cerebral artery blood flow in a normal pregnancy?
The peak corresponds to systole of the heart and during diastole the flow is negative (or reduced)
What happens to the middle cerebral artery blood flow in foetal growth restriction?
The blood flow is maintained during both systole and diastole – increasing blood flow.
