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BSc Embryology > Practical 3 - Placentation and twinning > Flashcards

Practical 3 - Placentation and twinning Flashcards

1
Q

When and why does the placenta start to develop?

A

The beginning of week 4
- large increase in foetal demand

Major change at week 9
-increased SA to facilitate exchange - villi

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2
Q

From which cell line does the placenta develop

A

Trophoblast and extraembryonic mesoderm (chorionic plate) = foetal component

Uterine endometrium = maternal components

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3
Q

What is the difference between cytotrophoblast and syncitiotrophoblast

A

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

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4
Q

What are the layers of amniotic sac

A

amnion - foetal side
Chorion - outermost foetal mmbr (trophoblast & extraembryonic; mesoderm)

Decidua basalis: maternal side

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5
Q

How many vessels does the umbilical cord contain

A

2 x Umbilical artery
= supply deoxygenated blood of foetus to placenta

1 x umbilical vein - oxygenated blood - placenta –> embryo

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6
Q

What are the features of the normal full term placenta

A

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
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7
Q

What are the hormonal functions of the placenta

A

End of fourth month - sufficient progestrone to support pregnancy

First two months - hCG - maintains corpus luteum - probabaly synthesized in syncitiotrophoblast

Oestrogenic hormones - estriol

Somatotropin

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8
Q

Where does gas exchange occur in the placenta

A

-

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9
Q

What substances can cross the placenta

A 
O2
CO2
Hormones 
Amino acids
Carbohydrates 
Free fatty acids
Maternal antibodies - IgG
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10
Q

What are the three foetal shunts, when does each close

A

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

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11
Q

What becomes of the umbilical vein

A

Remains open at birth - closes in first week

Obliterates –> ligamentum venosum

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12
Q

What is the incidence of PDA

A

8/10,000

Normally, contraction of muscular wall after birth –> ligamentum arteriosus

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13
Q

Why are NSAIDs contraindicated in late pregnancy

A

Ass. w/ risk of premature closure of FDA and oligohydramnios
- inhibit COX1/2 - rate limiting enzymes for prostaglandins synthesis

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14
Q

What is a hyatidiform mole

A

Molar pregnancy

  • diploid - only paternal chromosomes
  • abnormal blastocyst (hypoplasia) - some syncitiotrophobalst only
  • blastocyst demise, trophoblast develops

Placental mmbr with little/no embyro

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15
Q

What does the genetics of a molar pregnancy suggest

A

Paternal genes regulate trophoblast development

Formed by fertilisation of oocyte with no nuleus , duplication of male chromosomes

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16
Q

What are the RF for molar pregnancy, how common is it?

A

1/1000

previous molar preg
Age < 20, >35

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17
Q

How do you detect a molar pregnancy

A

USS- snowstorm

Bloods - hCG Raised

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18
Q

What might molar pregnancy progress to

A

Ectopic choriocarcinoma

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19
Q

What is placenta previa and its RF

A

Low lying placenta
1/200

>1 child
C section 
Uterine surgery
Multiple pregnancy
Cocaine 
Smoking
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20
Q

What are the complications of placenta previa

A

Haemorrhage
Maternal and foetal death
Preterm

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21
Q

How is placenta detected prenatally and managed

A

USS

Mx-

  • depends on amount of bleeding, if it stops, maternal health, foetal health
  • C section
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22
Q

What is placenta accreta, what are the RF

A

absence of decidua basalis
Placental attachment to myometrium

RF:

  • Previous uterine surgery
  • Placental position (placenta previa)
23
Q

What are the consequences of placenta accreta

A

Post natal haemorrhage
-DIC, ARDS

Prem birth

24
Q

What is placental abruption, what are the RF

A

Partial placental detachment from myometrium
1/200

RF:

  • Smoking
  • Preeclampsia
  • Prior abruption
  • Trauma
  • Cocaine
  • Previous section
25
Q

How does placental abruption present

A

Acutely

  • Sudden onset abdo pain
  • Contractions (continuous)
  • PV bleed
  • Enlarged uterus disproportionate to gestational age
  • Decreased foetal movement and HR
26
Q

How is placental abruption managed

A

<36 weeks
No signs of foetal or maternal distress
Monitor in hospital

If foetus mature, foetal or maternal distress –> immediate delivery

27
Q

What is vasa previa and its incidence

A

1/1200 - 1/5000

Blood vessels unprotectd by placental tissue or umbilical cord

28
Q

How is vasa previa detected and managed

A

Vaginal exam
- pulsating foetal vessels in internal os
OR
-Dark PV bleed & foetal compromise

Urgent delivery
-60% mortality if PV bleed - foetal compromise

29
Q

What is the prognosis for Vasa Previa

A

If diagnosed antenatally
- 95% survival

If undetected
- likely rupture

30
Q

What is preeclampsia

A

HTN & proteinuria in pregnancy

~5%

31
Q

What are the risk factors of preeclampsia

A 
Pre-existing HTN 
SLE or Anti-phospholipid syndrome 
Previous Hx 
FHx 
>40yrs d 
>= 10 yrs between pregnancy 
BMI >= 35
32
Q

What are the signs and symptoms of preeclampsia

A

Symptoms

  • headache
  • confusion
  • Hx Convulsion
  • Respiratory symptoms
  • Visual disturbances
  • N&V

Signs

  • RUQ pain
  • Decreased urine output
33
Q

What is HELLP syndrome

A

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

34
Q

What is the major underlying cause of preeclampsia

A

Incomplete differentiation of cytotrophoblast cells
- many don’t undergo epithelial to endothelial transformation

Rudimentary invasion of spiral arteries

35
Q

What is eclampsia and how is it managed

A

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
36
Q

What is cord prolapse, how is it managed

A

Cord protrudes into vagina

Knee to chest position - shift foetus out of pelvis
- globes hand to push foetus upwards

37
Q

What is monozygotic twinning?

How might the membranes by arranged?

A

Twins derived from same oocyte
- identical twins

Diamniotic dichorionic
Diamniotic monochorionic
Monoamniotic monochorionic

38
Q

What is dizygotic twinning?

A

Fraternal twinning

  • 90%
  • 2 embryos from 2 separate ova, fertilised by 2 sperm
39
Q

Which type of twinning is most dangerous

A

Monozygotic monochorionic monoamniotic

- cord entaglement

40
Q

Why are the cotyledons inspected

A

Retained placental tissue

41
Q

What are complications of multiple pregnancy

A

TTTS
PRETERM
gestational HTN and diabetes

42
Q

What types of conjoined twins are most common

A

Thoracopagus - 20-40%
Omphalopagus - 13-33%
Pyopagus - 18-28%

43
Q

What is foetal hydrops

A

Accumulation of fluid in two or more compartments
Jaundice

Haemolytic disease of the newborn

44
Q

What is haemolytic disease of the newborn

A

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

45
Q

How is haemolytic disease of the newborn prevented

A

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

46
Q

What is the oxygen saturation of umbilical vein

A

80%

47
Q

What is the oxygen saturation of the umbilical arteries

A

58%

48
Q

When does the ductus venosus close

A

A few minutes post-natally, functional closure

Actual obliteration 2-3 months post-natally

49
Q

When does the foramen ovale close

A

Properly fuses about 1 year after birth, although mostly closed immediately

50
Q

When does the ductus arteriosus close

A

Almost immediately
-mediated by bradykinin

complete obliteration is thought to take 1-3 months

51
Q

What is the incidence of patent foramen ovale

A

25%

52
Q

What is the most and least common arrangment of mmbr

A

MOST:
Monochorionic, diamniotic
(Splitting at early blastocyst)

Diamniotic, dichorionic

LEAST:
-monoamniotic, monochorionic
(splitting at bilaminar disc stage)

53
Q

What are some complciations of twins in utero

A 
Cord entanglement 
TTS
Twin reversed arterial perfusion
Abnormal amount of amniotic fluid
Vanishing twin
Conjoined twin 
Foetus in fetu

BSc Embryology (7 decks)

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