What are the causative factors of maternal changes during pregnancy?
High levels of steroids (oestrogen & progesterone)
Mechanical displacement
Fetal requirements
What are the repercussions on different systems after pregnancy?
Pregnancy is a physiological event. Systems (usually) return to normal after delivery, but not all
How would we identify an abnormal pregnancy?
To diagnose abnormality in pregnancy need to detect changes in the changes
Why may pregnancy make it difficult to identify disorders?
Pregnancy may:
- exacerbate a pre-existing condition
- uncover ‘hidden’ or mild condition
What main events do pregnancy changes occur to cope with?
Changes designed to cope with several main events:
- increase in size of the uterus
- increased metabolic requirements of uterus
- structural and metabolic requirements of fetus
- removal of fetal waste products
- provision of amniotic fluid
- preparation for delivery and puerperium
What systems undergo maternal changes during pregnancy?
energy balance respiratory system cardiovascular system gastrointestinal system urinary system endocrine system
What placental peptides cause maternal changes?
placental peptides
hCG, hPL, GH
What is the role of maternal steroids?
placenta takes over ovarian (CL) production around wk 7
Name the maternal and foetal steroids
progesterone, oestradiol, oestriol
What are the maternal and fetal pituitary hormones?
GH, thyroid hormones, prolactin, CRF
What systems do the placental steroids affect?
- renin/angiotensin system
- respiratory centre
- GI tract
- blood vessels
- uterine myometrial contractility
How does weight change across pregnancy?
> total gain in weight 12.5-13kg Fetus 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
How is an energy balance maintained during pregnancy?
Energy output and storage is increased
Why is energy output increased?
to cope with increased respiration and cardiac output
Why is energy storage increased?
for fetus
for labour and puerperium
Why does fat and protein stores increase by 4-5 kg?
increased consumption and reduced use
mainly laid down in anterior abdominal wall
utilised later in pregnancy and puerperium
How much does the metabolic rate rise by during gestation?
350 kcal/day mid gestation 75% fetus and uterus
250 kcal/day late gestation 25% respiration(H&L)
What is the significance of glucose during pregnancy?
- need increased availability in 2nd trimester
- active transport across placenta as fetal energy source
- fetus stores some in liver
Descrube the maternal reserves of glucose in the 1st trimester
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)
Describe he fetal glucose reserves in the 2nd trimester
2nd Trimester Fetal reserves hPL causes insulin resistance ie less glucose into stores = increased availability in serum glucose (more crosses placenta) but can cause diabetes
How is the RAAS system affected during pregnancy?
Total water gain
E₂ and particularly P act on renin angiotensin system
Retain fluid better and thirst increases. Plasma levels increase - common for oedema to occur
Albumin levels drop decreasing oncotic pressure
How is respiration affected during gestation?
Oxygen consumption is increased
Bigger deeper breaths taken more frequently causing a 40% increase in minute volume → larger Oxygen pressures in arteries removal of more CO2
Facilitates gas transfer for baby
What is haemodilation?
The apparent anaemia as concentration of Hb falls
How does maternal blood adapt for gestation?
increased efficiency of iron absorption from gut
Also changes in white cells (up) and clotting factors..blood becomes hypercoagulable = increased fibrinogen for placental separation, but increased risk of thrombosis
Describe fetal blood
Fetal blood = increased Hb and altered in type → Increased O binding → oxygen given up by maternal Hb
What is the effect of smoking on fetal blood?
smoking increases maternal carboxy-Hb which is more permanent and reduces the increased binding = fetal hypoxia
What effect does the expanding uterus have on the heart?
pushes heart round
changes ECG and heart sounds
Why does pregnancy cause an increased CO?
increased heart rate and stroke volume
begins as early as 3 weeks to max 40% at 28 weeks
for maternal muscle and fetal supply
How is vasculature affected by pregnancy?
Increased cardiac output and vasodilation by steroids = Reduced peripheral resistance
Where is there increased blood flow to during pregnancy?
uterus placenta muscle kidney skin
How does the body adjust for heat loss during pregnancy?
Neoangiogenesis including extra capillaries in skin (spider naevi) to assist in heat loss
Describe the effects of progesterone on the GI tract
Progesterone causes relaxation of muscles especially uterus. Relaxes smooth muscle on gut - can cause constipation as transit time prolonged in gut.
Why is heartburn a common problem in pregnant women?
Also relaxes the lower oesophageal sphincter - in late pregnancy 3rd trimester, heartburn is a very common problem
Worsens as pregnancy goes on as uterus enlarges and pushes up on intestines
What is the significance of folic acid?
Folic acid vital for foetal wellbeing and DNA production
What disorder is folic acid deficiency associated with?
Deficiency linked to spina bifida- neural tube defect
How much folic acid is recommended to take?
Supplementation advised 5mg/ day up to week 12
How is the urinary tract affected by pregnancy?
Smooth muscle relaxation of urinary tract as well. Bladder, ureters and collecting systems in kidneys relax - dilated
What is a consequence of muscle relaxation of the urinary system?
Can cause urinary stasis causing UTIs
During pregnancy, how does increased CO affect the urinary system
If you have a 40-50% increase in CO => 40-50% increase in GFR → causes removal of urea and creatinine (v. low in pregnancy)
What causes an increase in urine frequency in the first trimester of pregnancy?
Urinary frequency is very common in first trimester of pregnancy
Uterus enlarges and pushes onto the back of the bladder
Describe the pressure on the bladder in the later trimesters of pregnancy
2nd trimester pressure eased off bladder
3rd trimester foetus head descends pushing onto bladder increasing urinary frequency
Why is the bladder so sensitive to uterine enlargement?
The bladder cannot distinguish between inside (trigone) or outside pressure - causes increased weeing
Explain the chnage in uterine size
Huge increase in muscle mass
Huge increase in blood flow
placenta and uterus = 1/6 of total
14000 mls (but not solid!)
Why does the uterus expand during gestation?
As the baby grows, amniotic sac expands and uterus gets bigger.
Describe the structure of the uterus during the third trimester
3rd trimester (24 wks +) expansion from the cervix and lower part of the cervix is less muscular and more fibrous
Why is a lower cesarean section normally carried out
During cesarean a lower segment cesarean takes place as its more fibrous and less muscular - less bleeding
Why is the upper part of the uterus so muscular?
Towards top of uterus is very thick and muscular for pushing baby out
What is the primary function of the cervix during pregnancy?
primary function is to retain the pregnancy
How does the cervix change during pregnancy?
Increase in vascularity Tissue softens from 8 weeks - changes in connective tissue - begins gradual preparation for expansion Proliferation of glands
What are the effects of gland proliferation?
mucosal layer becomes half of mass
great increase in mucus production
Progesterone causes thickening of cervical mucus plug protective..ie anti-infective
How does the body return to normal?
- Dramatic and rapid fall in steroids on delivery of the
placenta - Most endocrine-driven changes return to normal rapidly
- Uterine muscle rapidly loses oedema but contracts
slowly: never returns to pre-pregnancy size - Removal of steroids permits action of raised prolactin on
breast