Placental Development and Physiology + Multiple Pregnancy Flashcards
What is kind of disease is pre-eclampsia and what causes it?
Multi-organ disease, placenta
When is pre-eclampsia cured?
After birth
Why does gestational diabetes cause a large baby?
Bc glucose stimulates growth in baby
What consequence can gestational diabetes lead to?
Stillbirth
What keeps the early embryo alive?
Decidua
Describe placental morphogenesis
1) The placenta develops over the entire surface of the chorion and then at 16 weeks regresses to form the discoid placenta
2) Elevated levels of oxidative stress in the peripheral regions of normal pregnancies leads to villous regression and formation of the smooth chorion leavae (hyper oxygenation at the top)
Describe the early placenta
Completely envelops the embryo
Describe the early embryo
Very anoxic, surviving on only what is produced by granular cells in the early placenta
What can a functional MRI pick up on in a placenta?
Oxygen function and cervical softening
Describe the trophoblast plug
During early pregnancy the volume of the endovascular trophoblast is such that it plugs the mouths of the spiral arteries, preventing maternal blood flow into the placenta
What does the trophoblast plug coincide with?
The period of histiotrophic nutrition (diffusion, anoxic)
What is the histiotroph?
Nutritional material in spaces between the maternal and fetal tissues, derived from the maternal endometrium and the uterine glands, not from maternal blood flow
How thick is the maternal endometrium at 6 weeks?
5-6mm with highly active glands
What is the decidua?
Thick endometrium
Name 3 angiogenic factors active in early fetal and placental growth
1) VEGF = vascular endothelial factor
2) hCG = human chorionic gonadotrophin
3) hPL = human placental lactogen
Describe the action of progesterone in early fetal and placental growth
1) Progesterone stimulates glands (decidual cells) which produce prolactin
2) Prolactin stimulates glandular epithelium cells to produce the angiogenic factors, stimulating growth and proliferation of the embryo (and placenta?)
What are the 4 functions of the placenta?
1) Respiratory organ (controls gas exchange)
2) Nutrient transfer
3) Excretion of fetal waste products (like kidney)
4) Hormone synthesis
Describe the structure of the placenta at term
- Lobules in placenta, intercepted by septum
- Frongs contain smaller blood vessels from umbilical arteries and veins, essential for getting nutrients from mother to baby
What is the syncytiotrophoblast?
Line of cells between septum and villi with umbilical vessels highly specialised for transport
When does maternal and fetal blood come into direct contact?
Only at birth
Describe the transfer of blood from mother to fetus
Mother’s blood comes through arteries → syncytiotrophoblast → fetal circulation
How does maternal uterine blood flow changes with gestational age?
It increases greatly
Describe cells of the syncytiotrophoblast
- Syncytium (connected)
- Large nuclei
- No cell walls
- Brush border like kidney and gut (transport)
Why does the fetus still exist at a low pO2 (no more than 30) even after the initial hypoxic stage?
To protect from oxidative stress (more pCO2)
Describe the placental gas exchange gradient
Big gradient from mother to baby
Does maternal and fetal blood have the same or different buffer?
Same - placenta controls the pH of placental blood via bicarbonate buffer (acid base balance)
What is a big reason for SGA at birth?
Lack of transport of amino acids due to gene problems with transporters
Is there a net transport of amino acids to the fetus?
Yes
Why in developing countries do we want to improve the nutrition of mother before she conceives?
To prevent fetal growth restriction (FGR) → main problem is issue with placenta e.g. anaemia and protein deficiency
What does there need to be for implantation to happen?
Low oxygen tension
What would a gap in the placenta on US suggest?
Bleeding
What happens to the placenta in pre-eclampsia and FGR?
1) Placental villous tree has fewer branches bc of altered blood flow characteristics
2) Spiral artery remains narrowed
What is PI on a uterine artery doppler?
(Vmax-Vmin)/Vmax mean
What does increased PI increase the risk of?
Severe pre-eclampsia
When is severe IUGR best predicted in low-risk patients?
Second trimester by an increased PI
Can you pick up people likely to have a PE early (at 14 weeks)?
Yes but can’t prevent it - looks like a non-pregnant scan
What are monozygotic twins?
From one egg, identical (incidence = 3:1000 deliveries)
What are dizygotic twins?
Two eggs, non-identical (incidence of spontaneous dizygotic twins = 1:80)
What are risk factors for dizygotic twins?
1) Peak age 35-40 years - FSH rises, biological advantage of double ovulating, more chance of at least one succeeding
2) FH
3) Previous multiple birth
4) Increased BMI
5) Parity
6) Summer and autumn conceptions
7) Smoking
8) COCP
What are the three types of monozygotic twins (can see on US)?
1) Dichorionic, diamniotic - cleavage before implantation, two placentas, two amniotic sacs
2) Monochorionic, diamniotic - cleavage at day 6-8, one placenta, two amniotic sacs
3) Monochorionic, monoamniotic - cleavage after day 8, one placenta, one amniotic sac, 4%
What causes conjoined monozygotic twins?
Divide of placenta happens even later
What increases the risk of monozygotic twins?
IVF
What type of twins can be dichorionic and what type can be monochorionic?
1) Dichorionic - can be monozygotic or dizygotic
2) Monochorionic - can only be monozygotic
What is the most common combination for triplets?
Pair of monozygotic twins and a dizygotic
