T2 L17: Placenta & Intra-Uterine Growth Restriction, Abnormal Fetal Development

Question 1

what happens in days 4-5 in development of the zygote

Answer 1

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.

Question 2

what happens in days 6-7 in development of the zygote

Answer 2

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

Question 3

what happens in days 16+ in development of the zygote

Answer 3

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.

Question 4

describe the embryo in 3 germ layers

Answer 4

The hypoblast degenerates. The epiblast gives rise to all three germ layers.

The embryo folds to create the adult pattern

Question 5

look at slide 9

Answer 5

how was it

Question 6

describe the formation of the placenta

Answer 6

Syncytiotrophoblast invades decidua (endometrium)

Cytotrophoblast cells erodes maternal spiral arteries and veins

Spaces (lacunae) between the fill up with maternal blood

Followed by mesoderm that develops into fetal vessels

Aiding the transfer of nutrients, O2, across a simple cellular barrier

Question 7

look at slide 11

Answer 7

how was it

Question 8

describe the difference between CTB and STB cells

Answer 8

Cytotrophoblast cells (CTB):
Undifferentiated stem cells

Invade the maternal blood vessels and destroy the epithelium

Give rise to the syncytiotrophoblast cells (STB)

Reduce in number as pregnancy advances

Syncytiotrophoblast cells (STB):

Fully differentiated cells

Direct contact with maternal blood

Produce placental hormones

Question 9

what is the function of the placenta as an endocrine organ

Answer 9

maintenance of corpus luteum of pregnancy

progesterone and oestrogen

Human placental lactogen HPL:

growth, lactation

carbohydrate and lipid
Many more!

Question 10

describe the placental barrier

Answer 10

Maternal blood in the lacunae in direct contact with syncytiotrophoblasts

Mono layer of syncytiotrophoblast/cytotrophoblast/fetal capillary epithelium is all that separates the fetal and maternal blood

Cytotrophoblasts decrease as the pregnancy advances (not needed)

The barrier thins as pregnancy advances leading to a greater surface area for exchange (over 10m2 )

Question 11

what components are transferred across the placenta

Answer 11

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

Question 12

look at slide 16

Answer 12

how was it

Question 13

what is the Vasa praevia

Answer 13

velamentous cord insertion that runs across the cervical os

The fetal vessels within the umbilical cord pass over the internal os. As the internal os dilates in labour the vessels are stretched and exposed and can rupture leading to massive fetal blood loss and death.

Question 14

what are the clinical aspects of the placenta

Answer 14

Position of the placenta within 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)

Placenta Praevia

-Massive bleeding in pregnancy
-Painless bleeding
-Fetal death
Maternal death

Question 15

what does failure of trophoblastic invasion into maternal circulation at 12 & 18 weeks

Answer 15

• Poor maternal fetal mixing of blood
• Lack of oxygen and nutrients to the fetus
• Leads to Fetal Growth Restriction
• Pre-eclampsia (raised Blood Pressure)

Question 16

look at slide 22-23

Answer 16

how was it

Question 17

what is placental abruption

Answer 17

Massive bleeding in pregnancy (often concealed)

Extremely painful

Fetal death

Maternal death

Question 18

look at slide 25

Answer 18

how was it

Question 19

what is the difference between development and growth

Answer 19

First 12 weeks fetal development occurs – organs formed

Then the baby needs to get bigger – fetal growth

Question 20

what are the 2 types of growth problems

Answer 20

1-Small for gestational age (SGA)
<5th centile
normal variant or growth restricted

2-Intra-uterine growth restriction (IUGR)
<5th centile
growth restricted (i.e. failure to achieve growth potential)

Question 21

look at slide 5 IUGR

Answer 21

how was it

Question 22

what can fetal growth restriction result in

Answer 22

Deficient placental invasion

Reduced placental reserve

Fetal need exceeds supply

IUGR

Hypoxia

Fetal vascular redistribution

Oliguria

Abnormal CTG

Fetal death

Question 23

how can you diagnose IUGR

Answer 23

Clinical suspicion – abdomen “looks smaller”

Clinical measurement of uterine size: Symphysis - fundal height (SFH)

Question 24

what is symmetrical growth restriction and why does it occur

Answer 24

both head and abdominal growth affected

Chromosomal anomaly (T21)

Viral infection (Rubella, CMV)

Severe Placental insufficiency

OR normal small baby (look at the parents)

Question 25

look at slides 9 10 12 & 13

Answer 25

how was it

Question 26

what is asymmetrical growth restriction and why does it occur

Answer 26

Asymmetrical Growth Restriction: just abdominal growth affected

Abdominal circumference reflects the size of the fetal liver

Causes:

Placental insufficiency – no excess glycogen being deposited within the liver

Question 27

what are the consequences of hypoxia in the fetus

Answer 27

Blood flow (oxygen and nutrients) redirected to areas of greater importance
-Brain

Blood flow (oxygen and nutrients) redirected away from areas of lesser importance

• Gut (doesn’t eat!)
• Kidneys (placenta clears waste products)
• Lungs (placenta brings O2)

Question 28

what do you find in US in IUGR

Answer 28

• 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

Question 29

what are the clinical features of IUGR

Answer 29

• SFH smaller than expected
• Baby’s movements lessen to conserve energy
• Fetal heart rate changes as hypoxia develops (as seen on CTG)
• Fetal death

Question 30

when do you wait or deliver in IUGR

Answer 30

wait- Low chance of survival

To give steroids

Reduce need for C/S

Deliver- >32 weeks

Doppler abnormality

Decreased movements

CTG abnormality

Question 31

what is the action of Betamethasone/dexamethasone

Answer 31

• When given to the mother will cross the placenta and stimulate the aveoli cells to produce surfactant gene
• Surfactant 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
• Produced from 24- 34 weeks and usually the baby will have enough by 34 weeks in preparation for a term delivery
• In premature babies it is lacking

Question 32

look at slides 20-22

Answer 32

how was it