Maternal changes in pregnancy Flashcards
What are the causative factors of pregnancy?
- high levels of steroids
- mechanical displacement
- foetal requirements
Pregnancy is a physiological event. The systems (normally) return back to normal after delivery, but not all of them.
How would we diagnose an abnormality in pregnancy?
To diagnose an abnormality in pregnancy, we need to detect changes within the changes.
However, pregnancy may:
- exacerbate a pre-existing condition
- uncover a ‘hidden’ or mild condition
What do the changes that occur during pregnancy cope for?
- increase in the size of the uterus
- increased metabolic requirements of the uterus
- structural and metabolic requirements of the foetus
- removal of foetal waste products
- provision of amniotic fluid
- preparation for delivery and puerperium
List the systems in which the changes can occur
- cardiovascular system
- respiratory system
- gastrointestinal system
- urinary system
- endocrine system
- energy balance
Which hormones cause most of the changes?
Placental peptides:
- hCG
- 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
- CRF
Where do the effects of placental steroids take place?
- renin/angiotensin system (RAAS)
- respiratory centre
- GI tract
- blood vessels
- uterine myometrial contractility
Summarise the weight gain that occurs during pregnancy
The total weight gain is 12.5 to 13 kg.
Foetus plus placenta: 5 kg Fat and protein: 4.5 kg Body water: 1.5 kg Breasts: 1 kg Uterus: 0.5-1 kg
Ideally, the gain is kept to less than 13kg; failure to gain the weight or a sudden change needs monitoring.
How does energy balance change during pregnancy?
We need to increase our energy:
OUTPUT:
- to cope with the increased respiration and cardiac output
and STORAGE:
- for the foetus
- for labour and puerperium
We gain 4-5kg in fat and protein stores. The reasons for this are:
- increased consumption and reduced use
- mainly laid down in the anterior abdominal wall
- utilised later in pregnancy and puerperium
What are some requirements for glucose during pregnancy?
We need:
- an increased availability of glucose in the second trimester
- active transport across the placenta as a foetal energy source
- foetus storing some glucose in its liver
How is glucose stored and utilised during pregnancy?
During the first trimester we used maternal reserves:
- pancreatic β cells increase in number
- plasma insulin increases
- fasting serum glucose decreases (laid down as stores and used by muscles)
During the second trimester, we use foetal reserves:
- hPL causes insulin resistance (ie. there is less glucose going to stores)
- there is increased availability of serum glucose (thus more crosses the placenta, however, it can cause diabetes)
Where does all water gain come from?
The water gain during pregnancy can account for up to 8.1 litres, coming from:
- foetus
- placenta
- amniotic fluid
- oedema (lungs, connective tissue, ligaments, leakage, swollen ankles)
- uterine muscles
- mammary glands
- plasma volume
How do we increase the plasma volume during pregnancy?
- sodium retention
- resetting of the osmostat
- decreased thirst threshold
- decrease in plasma oncotic pressure (albumin)
(E2 and P act on the renin-angiotensin system)
How do E2 and P increase O2 consumption?
E2 and P increase the respiratory centre sensitivity to CO2. The thoracic anatomy of the mother also changes, with the ribcage displacing upwards and the ribs flaring outwards.
These factors cause the mother to breathe more deeply, causing the minute volume to decrease by about 40%.
Thus, the arterial PO2 increases (by about 10%), and the PCO2 decreases (by about 15-20%).
This facilitates gas transfer between the mother and the foetus.
How does maternal blood composition differ from normal composition?
The maternal plasma volume increases by about 40-50%, and the red cell mass increases by about 18-20%.
There is also an increase in white cells and clotting factors.
Due to the changes in volume and red cell mass, the haemoglobin concentration actually decreases. This is a phenomenon called haemodilution, where there is apparent anaemia due to the concentration of Hb falling, not the amount.
To make all the additional red blood cells, there is an increased efficiency of iron absorption in the gut.
Due to the increase in white blood cells and clotting factors, the blood becomes hypercoagulable. This means we will have increased fibrinogen for placental separation, but an increased risk of thrombosis.
How is foetal blood able to take oxygen from the mother’s blood?
Foetal blood has increased haemoglobin and an increased type. This increases O2 binding.
Thus, oxygen is given up by the maternal Hb.
