Flashcards in Pregnancy Deck (21)
What is the absolute limit of survival outside the womb without external help?
27 weeks (end of the 2nd trimester)
How common are miscarriages?
High rates of spontaneous miscarriage during the 1st trimester.
List some maternal changes that occur during the 1st trimester and later.
- altered brain function
- altered hormones
- altered appetite
- altered emotions
- altered immune system
List some maternal changes that occur during the 2nd trimester and later.
- altered fluid
- increased blood volume
- increased blood clotting
- decreased blood pressure
List some maternal changes that occur during the 3rd trimester.
- increased weight
- altered joints
What is hCG?
Human chorionic gonadotrophin - key hormone in pregnancy. It is an LH analogue and so drives the production of oestrogens and progesterone.
How does hCG maintain pregnancy?
Progesterone is necessary to maintain pregnancy - hCG drives progesterone production from the corpus luteum.
How do levels of pregnancy hormones change?
- hCG peaks and falls in the 1st trimester
- oestrogens, progesterone and plasma lactogen all rise throughout pregnancy (reflecting the increasing size of the placenta)
Which structures produce steroids throughout pregnancy?
For the first couple of months, it is the role of the corpus luteum. Then the placenta takes over.
What happens to levels of LH and FSH?
Levels of both hormones decrease substantially due to the high levels of steroids suppressing the HPG axis.
What is the main risk to maternal health?
Risks during delivery (health is relatively unaffected by pregnancy)
List the stages of development of the fertilised egg.
Conceptus - everything resulting from the fertilised egg (baby, placenta, fetal membranes, umbilical cord)
1. Embryo - the developing baby before it can be recognised as human
2. Foetus - the baby for the rest of pregnancy (it can be recognised as clearly human at around weeks 9-12)
3. Infant - normally applied after birth, as less clear
What is the normal timing of labour (term) during a pregnancy?
37-41 weeks (although 39-40 weeks is normally expected). Either side of this is pre- or post-term delivery.
How is term determined?
- take the first day of the last menstrual period
- we can then work out when the woman ovulated (2 weeks later)
Embryologists use the first day as the point of fertilisation - this only causes a variation of 2 weeks in term dates.
Describe the basic structure of the placenta.
It is sub-divided into cotyledons (30-60 per placenta). Each cotyledon contains one or more villi.
The placental villi have a very large surface area for exchange. The placenta is also anchored to the maternal decidualised endometrium.
List some functions of the placenta.
- separation of blood supply of mother and baby
- exchange of nutrients (mother to foetus) and waste products (foetus to mother)
- biosynthesis of hormones
Describe the structure of villi in the placenta.
Within each villus is a complex blood supply (arterial and venous vessels connected to capillaries in the terminal portions). The arterial system contains deoxygenated blood, whilst the venous system contains oxygenated blood.
Describe the basic development of the placenta.
It begins as a single layer of cells in the blastocyst. These proliferate and differentiate to form a simple branched structure, which expands to form sprouts.
Describe the development of the villi.
1. 9 days after fertilisation, the conceptus is fully implanted into the endometrial lining. The outer layer is multinucleated syncytiotrophoblasts, which contain fluid-filled lacunae.
2. The underlying layer of cytotrophoblast proliferates adjacent to the embryo - this is where the placenta will develop.
3. Following implantation, the cytotrophoblast proliferate into the syncytium.
4. First a columnar structure forms (cytotrophoblast column), which undergoes branching (villous sprouts).
At the centre of each villus are mesenchymal (extra-embryonic mesoderm) cells.
5. From these cells, the villus vascular system develops. The branching process continues through out pregnancy, giving rise to the complex branched villi.
How does blood flow allow passage of oxygen/nutrients from the mother's blood?
Oxygenated blood flows over the maternal surface of the placenta, allowing transfer of oxygen/nutrients to the foetal tissue. Deoxygenated blood flows away over the foetal surface, picks up the oxygen/nutrients and delivers it back to the foetus.