Pregnancy & Labour Flashcards
How many trimesters in pregnancy?
3
When is loss of pregnancy common and when does a foetus become viable ?
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Spontaneous loss of pregnancy in the first trimester is very common (1/3rd of all) but after that, loss is minimal.
The end of the 2nd trimester [∼24w] marks the limit of infant survival (after this, the child is viable).
o Modern care can push this back to 22 weeks.
What is term
Term (39-40 weeks) is expected delivery time and is stated as (40 weeks) since LMP.
Maternal Changes - When do abdominal changes become apparent?
Abdominal changes in the mother only become apparent during the 2nd trimester +.
Main maternal changes
Increased:
- Weight
- Blood clotting
- Vaginal mucus
- Hormonal levels
- Body temp
- Breast size
Altered:
- Appetite
- Joints
- Fluid balance
- Immune system
- Brain function
- Emotions
Decreased BP
Morning sickness
Start of Pregnancy?
- IVF timings and significance
Pregnancy is counted from the first day of the last menstrual period (LMP), with other events dated from this time.
IVF pregnancy timing – fertilisation occurs 2-3 days before:
o There will be a difference in time of 2-2.5w from the gestational age (GA, derived from LMP) and the GA in an IVF pregnancy – this can make a large difference when determining viability (22 vs 24 weeks for example).
Reasons for maternal changes - Increased weight
(+10-15kg) – baby, placenta, amniotic fluid, increased fluid retention, increased stores.
Maternal changes - Increased Hormone levels
o hCG – peaks 1st trimester and decreases thereafter.
o All other hormones (progesterone, oestrogens, placental lactogen) – slowly increase as the pregnancy progresses.
Importance of progesterone in pregnancy?
- progesterone antagonist effects
Progesterone is key to maintaining the pregnancy – progesterone antagonists loss of pregnancy at ALL gestational ages.
Importance of hCG?
hCG = a functional homologue of LH produced in pregnancy and drives production of oestrogens and progesterones from corpus luteum.
Progesterone source?
Progesterone source:
o Fertilisation → 8 weeks’ gestation – corpus luteum source via hCG.
o 8+ weeks – placenta supplies progesterone.
The change-over = “Luteo-placental shift”.
For understanding: hCG = a functional homologue of LH produced in pregnancy and drives production of oestrogens and progesterones from corpus luteum.
Oestrogen source?
o Fertilisation → Luteo-placental shift – corpus luteum (via hCG)
o 8+ weeks – complex interplay between foetal/maternal adrenals and placenta
Explain oestrogen source at
8+ weeks – (complex interplay between foetal/maternal adrenals and placenta)?
Human placenta – does not express the enzymes needed to convert pregnenolone → androgens so this occurs in foetal adrenals.
• The weak androgen produced (DHEA) is sulphated to give DHEA-S which is inactive (so female foetus is not exposed to androgens).
• DHEA-S goes to the placenta to be converted to 17β-oestradiol.
High levels of oestriol are produced by a parallel mechanism including hydroxylation of DHEA-S in foetal liver to give 16OH-DHEA-S.
FSH and LH throughout pregnancy?
High steroid levels supress HPG-axis → low FSH and LH throughout.
Maternal change:
Reasons for Increased blood clotting tendency?
Protective against losing blood at delivery.
Decreased blood pressure lowest when and significance?
Is lowest during 2nd trimester and is why pregnant women should not stand for long.
Reasons for Increased basal body temperature?
possibly by role of progesterone. Also, mediated by increased foetal size.
Increased breast size- when and why?
Changes start in 1st trimester and continue throughout – due to all hormones!
Increased vaginal mucus - nature of mucus?
Increased vaginal mucus – more clear mucus produced.
“Morning sickness” link and what is severe version called?
“Morning sickness” – affects 80%, more severe version is “Hyperemesis gravidarium”. Unknown cause but maybe linked to hCG levels being high in the first trimester.
Reasons for Altered brain function?
Due to high levels of steroids, such as progesterone.
Reasons for Altered appetite
Due to +height of fundus, stomach may be impinged and mother may need smaller meals
Reasons for Altered fluid balance and urination frequency?
Altered fluid balance and urination frequency – as kidney functions change → ~50%+ in plasma fluid volume by term. Increasing abdominal size also puts pressure on bladder so more frequent urination.
Reasons for Altered emotional state?
Due to hormone levels and can vary in people (e.g. happy post-natal depression).
Reasons for Altered joints?
Changes in pelvis to make connections more flexible to permit child-birth.
Altered immune system – 2 main points should be considered?
o Production of factors – supress the maternal immune system from the utero-placental interface. This results in a reduction of Th1 responses and increased Th2 responses.
o Placenta cells expresses unusual HLA – placental HLA are almost invariant (HLA-G has 5 known sequence variants – normal HLA-A and others have millions of variants) and very simple. This is thought to identify the tissue as human but due to its simplicity, no other information is given. HLA-G can also supress some leucocytes and down-regulate maternal immune responses.
Define conceptus, embryo, foetus, infant?
o Conceptus – everything resulting from the fertilised egg.
o Embryo – the baby up to week 8 of development.
o Foetus – the baby for the rest of pregnancy.
o Infant – applied after delivery typically.
Timings in embryology v.s pregnancy?
Again, remember that timings used to discuss embryology are usually from point of fertilisation, 2 weeks after LMP timings used in timings of pregnancy – the embryology timings are PF – Post-Fertilisation.
Weights of the foetus in the 3 trimesters and the viable weight range?
o First trimester – 50g.
o Second trimester – 1050g – viable at 500-820g stage (21-24 weeks).
o Third trimester – 2100g.
Chromosomal abnormalities?
o Too few sex chromosomes – Turner’s syndrome – 45 X0.
o Too many sex chromosomes – Klienfelter’s syndrome – 47 XXX, 47 XYY, etc.
o Too few autosomes – non-viability, as does 45 Y0 [no x chromosome – one is essential]
o Too many autosomes – Downs Syndrome – trisomy 21.
Most risks to the pregnancy occur when?
- main risks in 3rd trimester
Most risks to the pregnancy occur in the first trimester of pregnancy.
The main risks associated with pregnancy in the 3rd trimester is to do with the birth:
o There are 4 main organs (lungs, digestive system, immune system and brain) that have limited use in utero so late development is logical but problems developing here become apparent at birth.
This also may cause problems with pre-term birth.
Placental Functions
Separation between maternal and fetal vascular system
Exchange nutrients and waste products
Biosynthesis
Immunoregulation of whole of pregnancy [ensures no rejection of conceptus]
Connection: placenta must anchor the pregnancy in place
SEBIC
Anatomy of the Placenta
[insert digram]
- what is the primary sub-unit and what does it provide
- Foetal Veins and arteries in placenta
- What are Cotyledons and decidua
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Primary subunit is the placental villus that has the branches.
o This provides a large surface area for exchange between the maternal and foetal vascular systems.
Note that the veins contain oxygenated blood and the arteries contain deoxygenated blood as the placenta carries out a parallel function to the lungs during pregnancy.
Note the separation of the maternal and foetal systems despite being near.
Cotyledons – the maternal surface of the placenta is sub-divided into cotyledons. Each contains one or more villi.
(The gaps between cotyledon contains maternal tissue = decidua)
Development of the Placenta?
Approx. 9 days PF, the conceptus is completely implanted in the maternal endometrium.
- IMPLANTATION of conceptus into endometrial epithelium.
- Trophoblast layer of the conceptus forms 2 layers → cytotrophoblast (CTB, inner) and syncytiotrophoblast (STB, outer layer)
- Note: Placenta originates from the cytotrophoblasts layer. - STB sends out PROJECTIONS to embed onto the endometrium +
LACUNAE → form in STB gets filled with maternal blood. - CTB expansion into STB → PRIMARY CHORIONIC VILLI
- Mesoderm line (fill) these villi → SECONDARY CHORIONIC VILLI.
- Embryonic blood vessels form in the mesoderm → TERTIARY CHORIONIC VILLI
[Cytotrophoblasts proliferate into the syncytium to form a columnar structure which becomes a villous structure]
- CTB cells from the villi grow towards the decidua (maternal tissue between cotyledon) and form a CTB SHELL . This has plugs.
- ~6th week → the villi reach maternal spiral arteries → CTB invade the spiral arteries → SPIRAL ARTERY REMODELLING i.e. arteries become wide bore = greater exchange of nutrients
- ~10-12th week → CTB plugs breakdown and placenta exposed to full maternal blood flow.
[note: decidual gland hypertrophy supplies nutrients during 1st trimester - not maternal blood - maternal blood when plugs breakdown that block spinal arteries]
- The source of the nutrients (glands: histotrophic) rather than maternal blood (haemotrophic) is different
~10-12th week CTB plugs breakdown and placenta exposed to full maternal blood flow - subsequent risk of miscarriage?
If the placenta is not anchored properly, the increased pressure as it is exposed to the maternal blood supply can lead to a detach and a miscarriage.
The cytotrophoblast (ctb) cells remodel the spiral arteries during the 1st trimester [what happens]?
The remodelling converts the narrow bore spiral vessels into wide-bore vessels to transport more volumes of blood.
o The ctb cells replace the vascular endothelium and VSMCs which is important as it means the vessels here cannot respond to vasoconstrictors.
The placenta has no nerves so can be cut without harm
Regulation of Growth/Development of the placenta?
Placenta regulates its own growth/development through autocrine functions.
The maternal decidua mainly seems to restrain (modulate) placental growth/development so the placenta is optimal both for the baby and mother.
Maternal Risks in pregnancy?
Most risks to the mother lie in delivery and labour.
Risks:
o Remodelling of the spiral arteries means that vessels can lose relatively large amounts of blood after delivery – this should be limited by contractions of the uterus after the placenta has been delivered.
o Placenta must be checked carefully to make sure all has been delivered as it is quite inflexible and any left in the uterus may lead to ineffective uterine contractions.
Risks to infant in pregnancy and after ?
o Most severe risk is in defects in the gametes – chromosome irregularities.
- Loss of any autosome is not compatible with life miscarriage.
- Changes in sex chromosomes is generally less severe (loss is more serious than gain).
• Turners is a loss of a sex chromosome and leads to infertility.
o Infants born before 32w GA are at the greatest risk due to incomplete development of the 4 organs (brain, lungs, digestive and immune systems)
Risks associated with The placenta?
o Most serious problem is incomplete anchorage in the 1st trimester. Possibly due to:
Developmental problems.
Detachment in the late 1st trimester.
Note: Placental delivery after baby delivery is importnat.
Define Stillbirth?
Stillbirth – death of the infant within the uterus, so that it is delivered without signs of life.
o Some definitions include the viability limit (23w) so any dead births before this are miscarriages and any after this are stillbirths.
Detection of stillbirth?
Detection – via monitoring of foetal wellbeing:
o Ultrasound – monitor foetal movements.
o Foetal blood flow assessment – Doppler ultrasound.
