Pregnancy Flashcards
Pregnancy is divided into 3 trimesters - explain this and some key points
Pregnancy is divided into 3 trimesters
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 marks the limit of infant survival (after this, the child is viable)
• Modern care can push this back to 22 weeks
Term (39-40 weeks) is expected delivery time and is stated as ~280 days (40 weeks) since LMP
General changes during pregnancy?
Abdominal changes in the mother only become apparent during the 2nd trimester onwards
Main maternal changes seen?
o Increased weight o Increased hormone levels o Increased body temperature o Increased blood clotting o Decreased BP o Increased breast size o Increased vaginal mucus o “Morning sickness” o Altered brain function o Altered appetite o Altered fluid balance o Altered emotional state o Altered joints o Altered immune system
‘Altered’ - extent to which they change vary throughout pregnancy
What helps mark the start of pregnancy?
From the LMP
What is IVF pregnancy timing?
Fertilisation occurs 2-3 days before
• difference of 2-2.5 weeks from the gestational age derived from LMP vs. IVF
Hence can make a large different when determining viability (e.g. 22 vs. 24 weeks)
Why do mums increase in weight?
Baby, placenta, amniotic fluid, increased fluid retention, increased stores
+10-15kg
What changes in hormones are seen during pregnancy?
hCG
– peaks 1st trimester and decreases thereafter.
All other hormones (progesterone, oestrogens, lactogen)
– slowly increase as the pregnancy progresses.
Progesterone is key to maintaining the pregnancy
• i.e. progesterone antagonists = loss of pregnancy at ALL gestational ages
What is the source of PG in pregnant mothers?
Progesterone source:
Fertilisation –> 8 weeks’ gestation
– corpus luteum source via hCG
8+ weeks
– placenta supplies progesterone (as increases in size)
• the change-over = “Luteo-placental shift”.
What is the source of O in pregnant mothers?
Oestrogen source:
Fertilisation –> Luteo-placental shift
– corpus luteum
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 17-oestradiol
High levels of oestriol are produced by a parallel mechanism including hydroxylation of DHEA-S in foetal liver to give 16OH-DHEA-S.
High steroid levels supress HPG-axis
• LOW FSH & LH throughout
Explain some of the main maternal changes seen: x increased blood clot tendency x decreased BP x increased basal oC x increased breast size x increased vaginal mucus x 'morning sickness' x altered brain function x altered appetite
Increased blood clotting tendency
– protective against losing blood at delivery.
Decreased blood pressure
– is lowest during 2nd trimester and is why pregnant women should not stand for long.
Increased basal body temperature
– possibly by role of progesterone. Also, mediated by increased foetal size.
Increased breast size
– changes start in 1st trimester and continue throughout = due to all hormones!
Increased vaginal mucus
– more clear mucus produced.
“Morning sickness”
– affects 80%, more severe version is “Hyperemesis gravidarium”. Unknown cause but maybe linked to hCG levels being high in the first trimester.
Altered brain function
– due to high levels of steroids, such as progesterone.
Altered appetite
– due to +height of fundus, stomach may be impinged and mother may need smaller meals.
Explain some of the main maternal changes seen:
x altered fluid balance & urination frequency
x altered emotional state
x altered joints
x altered I.S
Altered fluid balance and urination frequency
– kidney functions change –> ~50%+ in plasma fluid volume by term. Increasing abdominal size also puts pressure on bladder so more frequent urination.
Altered emotional state
– due to hormone levels and can vary in people (e.g. happy –> post-natal depression).
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 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 used to discuss embryology?
Normally, from point of fertilisation
• 2 weeks AFTER LMP
Embryology timings are PF - post-fertilisation
Weight of foetus throughout pregnancy?
o First trimester – 50g.
o Second trimester – 1050g – viable at 500-820g stage (21-24 weeks)
o Third trimester – 2100g.
What are some chromosomal abnormalities that can develop?
Too few sex chromosomes
– Turner’s syndrome – 45 X0
Too many sex chromosomes
– Klienfelter’s syndrome – 47 XXX, 47 XYY, etc.
Too few autosomes
– non-viability, as does 45 Y0.
Too many autosomes
– Downs Syndrome – trisomy 21.
