Complications of Pregnancy and Labour

Question 1

What are the essential processes involved in implantation of the blastocyst?

Answer 1

1. The fertilised zygote migrates to the uterus and the blastocyst implants in the decidua
2. Early in development (first 8-10 weeks) the blastocyst is supported by uterine fluid secreted by uterine glands
3. At this stage in development the maternal blood supply would be highly damaging to the developing embryo as it is too high in oxygen- so extravillous trophoblast cells (EVTs) plug uterine arteries to prevent blood flow or circulation to the embryo at this stage
4. After this spiral artery remodelling takes place whereby the EVT cells degrade the smooth muscle cells around the uterine arteries and replace some endothelial cells with EVTs that act as pseudo-endothelial cells: this is the beginning of the formation of the placenta
5. At week 12 oxidative stress has increased for the foetus and they have synthesised antioxidants in time for theEVT plug that is blocking the spiral arteries that have undergone remodelling to be lost (as the arteries should be fully remodelled) and maternal blood will perfuse into the placenta

Question 2

Describe what goes wrong in preeclampsia:

Answer 2

• If some maternal uterine arteries are not adequately plugged with EVTs: the highly oxygenated maternal blood will enter the placenta too early and the uterine spiral arteries will not have been adequately remodelled (smooth muscle would not have been lost and endothelial cells replaced with EVTs)
• This early entry of maternal blood and the lack of spiral artery remodelling leads to preeclampsia later in the pregnancy (occurs after 20 weeks)
• If the situation is severe and the developing embryo is exposed to a lot of maternal blood early due to a lack of spiral artery plugging and remodelling there will be an instantaneous miscarriage
• The more smooth muscle that remains around these spiral arteries- the early the preeclampsia will develop

Question 3

What are the important antioxidants produced by the foetus to protect itself against the highly oxygenated maternal blood that perfuses the placenta in week 12?

Answer 3

• superoxide dismutase, glutathione peroxidase, and catalase among others
• In normal development, just as the antioxidant levels become high enough (due to oxidative stress) and the uterine secretions become insufficient- the EVT plugs are removed

Question 4

What are the important cell types for spiral artery remodelling?

Answer 4

1. Maternal- natural killer cells:
   - regulate EVT invasion by secreting interleukins, metalloproteinase, integrins etc.
2. Foetal: extravillous trophoblasts:
   - Invade the decidua
   - Line spiral arteries and replace endothelial cells

Question 5

What characteristics of AP and contractions of the myometrium are important for progressive labour?

Answer 5

• Action potentials must be able to plateau
• Slower action potentials give time for the uterine muscle to contract strongly
• There must be sufficient time between action potentials and contractions for fetal survival
• Oxytocin can be adminstered to slow action potentials and thus contractions and bring on labour

Question 6

What are some problems obesity can cause during pregnancy and labour?

Answer 6

• Prolonged pregnancy (they do not go in to labour)
• Need for labour induction and augmention
• Placental abruption (the placenta is torn away from the mother’s blood supply during delivery leaving the baby without oxygen)
• Failure to progress in labour
• 50% of obese women require C-sections
• Neonatal morbidity
• Higher risk of placenta previa and accreta

Question 7

What affect does age have on labour and delivery?

Answer 7

• The affect of age on labour and delivery is seen mainly in terms of first pregnancies
• It is women that over are over 35 that are having their first baby that are at a much higher risk of complication that women over 35 that have already had other children
• Older women with their first pregnancy are more likely to have K7 potassium channel changes resulting in them having a very high activity making the uterine tissue very negative in potential so it is very difficult for the membrane potential to reach threshold and produce the action potentials needed for contractions

Question 8

What is the role of hERG potassium channels and their relation to obese women?

Answer 8

• Blocking hERG potassium channels can help generate the slower, larger contractions needed for labour (in the same way oxytocin does)
• This is excellent as obese women often don’t respond to oxytocin
• In normal labour an inhibitory protein is sythesised to block hERG channels to allow for prolonged action potentials- but this does not occur effectively in obese women