3. Pregnancy + labour Flashcards
Which trimester are spontaneous miscarriages more likely in?
First trimester
What is the absolute limit survival outside the womb, without the intensive care unit?
27 weeks
What factor defines the end of the 2nd trimester?
Absolute limit of survival outside the womb (end of 27 weeks)
What happens to maternal blood volume, blood clotting tendency and blood pressure during pregnancy?
- Blood volume - increased
- Blood clotting tendency - increased
- Blood pressure - decreased
(all in 2nd trimester)
In which trimester is matenral brain function, hormones, immune system, appetite and emotional state altered?
1st trimester
What functional homologue of LH (driving oestrogens and progesterones production) is the key hormone of human pregnancy?
Human chorionic gonadotrophin
Where does hCG stimulate progesterone production from to keep the pregnancy going?
Corpus luteum
Which somatotrophin hormone increases as the size of the placenta increases?
Placental lactogen (oestrogens and progesterones show the shame pattern)
Which organ takes over oestrogen/progesterone production from the corpus luteum a few months into pregnancy?
Placenta
In which trimester are there peak hCG levels?
1st trimester (then declines after)
What happens to LH and FSH during pregnancy?
Suppressed by steroids negative feedback on HPG
Which part of pregnancy poses the biggest threat to maternal health and life?
Delivery process
What is a conceptus?
Everything resulting from ferilised egg (baby, placenta, umbilical cord etc.)
What is the expected timing of delivery?
- 39-40 weeks
* 280 days since the beginning of the last menstrual period
When do we establish ovulation, and what do embryologists use as the point of fertilisation?
- We take first day of the last menstrual period, and work out ovulation as 2 weeks after that day
- Embryologists take the first day as the point of fertilisation
2 week difference, but not huge difference in the scheme of term dates
Which gestational ages does ‘term’ cover?
37-41 weeks gestation
Any deliveries either side of these limits are pre-term or post-term
What are agents that can harm the development of an embryo or foetus?
Teratogen (more vulnerable earlier on in pregnancy)
What are the separations in the placenta called?
Cotyledons (30-60 per placenta)
What is the primary subunit of the placenta?
Placental villus
Describe the development of the human placenta?
- Conceptus is almost completely implanted within the endometrium (day 9 post-fertilisation)
- Outer layer is multinucletated syncytiotrophoblasts, containing fluid-filled lacunae
- Underlying cytotrophoblast is proliferating into the syncytium
- Columnar structure forms (cytotrophoblast column) which undergoes branching (villous sprouts)
- Mesenchymal cells at the centre of each villus - villus vascular system develops from these cells
- Branching continues
Why are there fewer cytrotrophoblasts at term?
For closer apposition between the syncytium and placental capillaries
Explain the remodelling of arteries in the placenta?
• Cytotrophoblast cells block spiral arteries - part of remodelling them
- limited oxygen supply could keep free radicals low
• Also involves loss of endothelium and smooth muscle cells of the arteries
• End up with distended, non-vasoactive vessels - can carry more blood at low pressure
• Allows high blood supply in trimesters 2 and 3 (greatest growth)
What does the cytotrophoblast do to the conceptus for 4 week post-fertilisation?
- Forms a shell around the conceptus
- Isolates it from maternal blood
- Shell remains in place for 8 weeks, plugging the spiral arteries
- Breaks down during week 10-12 starting with those at periphery of placenta
What initally provides the nutrients to the placenta and developing baby?
Decidual glands (hypertrophy)
