Maternal Changes in Pregnancy Flashcards
What are the changes of the uterus to cope with several main events of pregnancy?
Changes designed to cope with several main events:
- increase in size of the uterus - increased metabolic requirements of uterus - structural and metabolic requirements of foetus - removal of foetal waste products - provision of amniotic fluid of about a litre - preparation for delivery and puerperium (caring for your child through e.g. breastfeeding)
Which hormones cause most of the changes during pregnancy?
Placental peptides:
- hCG (keeps corpus luteum alive), hPL, GH
Maternal steroids
- placenta takes over ovarian (CL) production around week 7
Placental and foetal steroids
- progesterone, oestradiol, oestriol
Maternal and foetal pituitary hormones
- GH, thyroid hormones, prolactin, corticotrophin releasing factor (CRF)
What are the effects of placental steroids on different systems?
Steroids:
- renin/angiotensin system- steroids are structurally similar to aldosterone - respiratory centre- altered to get more oxygen in - GI tract- change to provide for your baby - blood vessels - uterine myometrial contractility
What weight changes are expected in an expecting mother?
Total gain in weight 12.5-13kg
Foetus plus placenta 5 kg
Fat and protein 4.5 kg
Body Water (this is excluding that in other listed structures)
1.5 kg intravascular
interstitial
intracellular
Breasts 1 kg
Uterus 0.5- 1kg
Ideally keep to less than 13kg: failure to gain or sudden change needs monitoring
What are the changes in energy balance when a woman is pregnant?
Need to increase energy
- Output
· to cope with increased respiration and cardiac output
- and storage
· for foetus
· for labour and puerperium
Gain in fat and protein stores 4-5 kg
- increased consumption and reduced use
- mainly laid down in anterior abdominal wall
- utilised later in pregnancy and puerperium
Basal Metabolic Rate
Rises by:
350 kcal/day mid gestation 75% foetus and uterus
250 kcal/day late gestation 25% respiration(H&L)
9 calories=1g fat therefore 40g fat for 350kcal i.e. 1 large Mars Bar
What are the changes in glucose usage and levels? What are the differences between the 1st and 2nd trimester?
Need increased availability in 2nd trimester
Active transport across placenta as foetal energy source
Foetus stores some in liver
1st Trimester Maternal reserves: pancreatic β cells increase in number plasma insulin increases fasting serum glucose decreases (laid down as stores and used by muscle) 2nd Trimester Foetal reserves: hPL causes insulin resistance I.e. less glucose into stores =increased availability in serum glucose so more crosses placenta But can cause diabetes
How do pregnant women gain total water weight?
Total Water Gain
E2 and P act on renin angiotensin system to activate it and make it stronger
There will be an increase of about 8.5L which go into several uses (in the diagram)
Sodium retention, resetting of the osmostat, decrease thirst threshold, decrease in plasma oncotic pressure (albumin)
Why is oxygen consumption increased during pregnancy?
You sex steroids have quite profound effects on your respiratory centre
They make it more sensitive to CO2
There’s also a change in the ribcage
You breathe more deeply
So your minute volume increases by 40%
Therefore your arterial PO2 increases by 10% and your PCO2 decreases by 15-20%
This is because if you have high maternal oxygen it will preferentially go down a diffusion gradient into foetal haemoglobin and obviously CO2, which will be high in foetal haemoglobin then goes down a gradient to low CO2
How is maternal blood different from regular?
Blood volume increases by about 45%, but varies from woman to woman
Increased efficiency of iron absorption from gut
Haemodilution= apparent anaemia as concentration of Hb falls so you’re not anaemic it just shows you are
Also increase in white cells (up) and clotting factors
Blood becomes hypercoagulable (so you don’t bleed to death when delivering)= increased fibrinogen for placental separation, but increased risk of thrombosis
What is foetal blood like?
Foetal blood is characterised by increased Hb and altered in type
This means there is increased oxygen binding
Therefore oxygen is given up by the maternal Hb
Smoking increases maternal carboxy-Hb which is more permanent and reduces the increased binding = foetal hypoxia
How does pregnancy change the heart?
Expanding uterus
- pushes heart round
- changes ECG and heart sounds
Increased cardiac output
- increased heart rate and stroke volume
- begins as early as 3 weeks to max 40% at 28 weeks
- for maternal muscle and foetal supply
How does pregnancy change the cardiovascular vessels?
Increased cardiac output and vasodilation by steroids= reduced peripheral resistance. Increased flow to : - uterus - placenta - muscle - kidney - skin Neoangiogenesis….including extra capillaries in skin (spider naevi) to assist in heat loss
How is the GI tract change during pregnancy?
Progesterone increases your appetite and thirst
Progesterone is also a smooth muscle relaxant which unfortunately reduces GIT motility which can lead to constipation
It also relaxes your lower oesophageal sphincter so what you get is some lovely acid reflux so people in their third trimester when its most prominent have small frequent meals
Why are most expecting mothers given folic acid?
Folic acid is very important for DNA production, growth and blood cells all throughout the utero-placental-foetal unit
So supplementation advised is 400mcg/day 3 months before getting pregnant up to week 12
A deficiency in folic acid has been linked to spina bifida and neuro tube defects
How is the urinary system changed during pregnancy?
Progesterone as mentioned is a smooth muscle relaxant so you get a very dilated kidney, ureter and bladder to a certain degree
Due to your dilated system you end up with a little bit of urine retained in your bladder or ureters leading to increased propensity for UTI
In the kidney, that 40-50% increased blood flow still has to go through the kidney so you get a 40-50% increase in glomerular filtration rate
This means you clear creatinine and urea and uric acid increasingly so normal reference ranges of levels cannot be applied
Most pregnant women experience urinary frequency because the uterus enlarging within the pelvis presses on the bladder
In the second trimester its lifted out of the pelvis so less pressure on bladder
In the third trimester the head descends down
