W6 - Maternal Changes in Pregnancy

Question 1

What are maternal changes in pregnancy?

Answer 1

Major changes in multiple systems
- Causative factors
»High levels of steroids - especially oestrogen, progesterone
»Mechanical displacement - expanding uterus
»Fetal requirements
- Pregnancy is a physiological event
- Systems (usually) return to normal after delivery, but not all!

Question 2

What is the maternal system in pregnancy?

Answer 2

• To diagnose abnormality in pregnancy need to detect changes in the changes!
• However, pregnancy may:
  »exacerbate a pre-existing condition - eg. high blood pressure
  »uncover ‘hidden’ or mild condition
• 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

Question 3

What are the systems in which changes occur?

Answer 3

l energy balance
l respiratory system
l cardiovascular system
l gastrointestinal system
l urinary system
l endocrine system

Question 4

Which hormones cause most of the changes?

Answer 4

• placental peptides
  »hCG, hPL, GH
• maternal steroids
  »placenta takes over ovarian (CL) production around
  wk 7
• placental and fetal steroids
  »progesterone, oestradiol, oestriol
• Maternal and fetal pituitary hormones
  »GH, thyroid hormones, prolactin, ‘Corticotrophin Releasing Factor’

Question 5

What are the effects of placental steroids?

Answer 5

Steroids:
»renin/angiotensin system
»respiratory centre
»GI tract
»blood vessels
»uterine myometrial contractility

Question 6

What is the total gain in weight?

Answer 6

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

Question 7

How is energy balanced?

Answer 7

l need to increase energy
»output
–to cope with increased respiration and cardiac output
»and storage
–for fetus
–for labour and puerperium
l 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
- Some exercise is beneficial, but as the months go by, exercise levels should decrease.

Question 8

What is the basal metabolic rate?

Answer 8

Rises by:
»350 kcal/day mid gestation 75% fetus and uterus
»250 kcal/day late gestation 25% respiration(H&L)

»9 calories=1g fat therefore 40g fat for 350kcal ie 1
large Mars Bar

Question 9

How is glucose affected?

Answer 9

*need increased availability in 2nd trimester
*active transport across placenta as fetal energy source
*fetus stores some in liver

1st Trimester
Maternal reservesMaternal reserves
pancreatic Beta cells increase in number
plasma insulin increases
fasting serum glucose decreases
(laid down as stores and used by muscle)

2nd Trimester
Fetal reservesFetal reserves
hPL causes insulin resistance
ie less glucose into stores
=increased availability in serum
glucose (more crosses placenta)
but can cause diabetes

Question 10

What is the total water gain?

Answer 10

-Plasma volume:
Sodium retention, resetting of the osmostat, decrease thirst threshold,decrease in plasma oncotic pressure (albumin).

• fetus
• placenta
• mammary gland
• uterine muscle
• amniotic fluid
• oedema - lungs connective tissue ligaments, leakage swollen ankles

Question 11

How is respiration - oxygen consumption increased?

Answer 11

Increases respiratory centre sensitivity to CO2.
Thoractic anatomy changes - ribcage is displaced upwards… ribs flare outwards. These changes enables more deep breaths. The minute volume increases 40%. Arterial PO2 increases and 10% PCO2 decreases 15-20%.
This means if you have your maternal and fetal blood side by side, which is what happens at the placenta, and you have high maternal oxygen, this will then go into a high diffusion gradient into the feta haemoglobin. The high in CO2 haemoglobin then goes down the conc grad into maternal cells.

Question 12

How is maternal blood changed?

Answer 12

Also changes in white cells (up) and clotting factors..blood becomes hypercoagulable = increased fibrinogen for placental separation, but increased risk of thrombosis.
Plasma goes up by around about 40-50%
This increases with twins, triplets etc
The red cell mass also goes up by 18-20%
This means the increased efficiency of iron absorption from the gut - need iron rich food!
The haemodilution = apparent anaemia as concentration of Hb falls.

Question 13

How does fetal blood exist?

Answer 13

Fetal blood= increased Hband altered in type -> increased
O2 binding -> Oxygen given up by maternal Hb

If the fetal haemoglobin has a higher affinity for binding to oxygen, the maternal oxygen can be given away far more easily.

smoking increases maternal carboxy-Hb, which is more permanent and reduces the increased binding = fetal hypoxia. This is a chronic effect. This is why babies of mothers that smokes, doesn’t grow very well.

Question 14

How is the cardiovascular system affected (heart)?

Answer 14

• 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 fetal supply

In woman, it is fairly common to have a heart murmur going through due to the additional volume. The more that goes in, the more that will come out. The stroke volume is what increases preferentially.

Question 15

How is the cardiovascular system affected (vessels)?

Answer 15

Increased cardiac output and vasodilation by steroids=
Reduced peripheral resistance.
Increased flow to :
* uterus
* placenta
* muscle
* kidney and
* skin
Neoangiogenesis….including extra capillaries in skin (spider naevi) to assist in heat loss

Question 16

How is the GI tract affected?

Answer 16

There is increased iron absorption. Progesterone is a major player. It affects appetite and thirst centres of the brain. You’d need to eat and drink a little bit more to expand that volume. There is reduced GIT motility - this can lead to constipation. It also relaxes lower oesophageal sphincter - acid reflux and heart burn are more common in the third trimester mainly because of the large uterus.

Question 17

What is the Dietary supplementation…folic acid for?

Answer 17

supplementation advised 5mg/ day up to week 12
deficiency linked to spina bifida- neural tube defect.

Folic acid is useful in DNA production, growth, blood cells in the uterus, placenta and fetus. Lack of folic acid was linked with things like spina bifida.

It is advised that to women planning pregnancy, start taking folic acid 400mcg/day, 3 months before stopping contraception. For people that has epilepsy for instance, their levels drop significantly, so their dosage is increased to 5mg a day. Take that up to about week 12, after the body plan of the baby is made, it is no longer needed.

Question 18

How is the urinary system affected?

Answer 18

Progesterone is again the major player.
It is a smooth muscle relaxant, so you get a very dilated kidney, ureter and bladder to a certain degree.

Problem with urinary tract infection - constantly flushing system and removing it. So if you have a dilated system, you can often end up with a little bit of urine retained in your bladder in the ureters. Pregnant women, because they have a relaxed system, has a higher propensity for urinary tract infections. This is why they always get their urine checked at the doctors - treated very quickly to prevent them getting unwell.

In the kidney, there is a 40-50% increase in blood flow meaning it all goes through the kidney - 40-50% increase in GFR too.

To measure, use: Creatinine, urea, uric acid
In normal pregnancy, these levels are extremely low, so a non-pregnant normal would not be normal in a pregnant person, because you are peeing them all away.

Question 19

How does the size of the uterus change?

Answer 19

huge increase in muscle mass
huge increase in blood flow
placenta and uterus = 1/6 of total

Early pregnancy: the uterus is enlarging, but it is within the pelvis compressing the bladder -> frequency. Always needing the bathroom.

Mid-pregnancy: The uterus is lifted out of the pelvis -> micturition normal.

At term: The head of the fetus descends into the pelvis -> frequency because the head is pressing against the bladder.

If you have a C-section, we call it a lower segment C-section. With the progression of pregnancy, the upper cervix and the very lower isthmic parts of the uterus changes a bit. The myometrium is where the movement comes from when you are in labour - that’s what pushes the baby down. Lower segment is less muscular and more fibrous. It acts as a funnel for the baby’s head to come down in labour because it is less muscular and less vascular when we cut into the C-section deliberately, we manipulate the knowledge about the uterus so it bleeds less at the time of C-section and it heals really well.

Question 20

What are the changes in the cervix?

Answer 20

• primary function is to retain the pregnancy
• increase in vascularity
• tissue softens from 8 weeks
  »changes in connective tissue
  »begins gradual preparation for expansion
• proliferation of glands
  »mucosal layer becomes half of mass
  »great increase in mucus production
  »protective..ie anti-infective

Sometimes if a woman gets a UTI, it can lead to premature labour.

Question 21

How does everything return to normal?

Answer 21

• Dramatic and rapid fall in steroids on delivery of
  the placenta
• Most endocrine-driven changes return to normal
  rapidly
• Uterine muscle rapidly looses oedema but contracts
  slowly: never returns to pre-pregnancy size
• Removal of steroids permits action of raised
  prolactin on breast. As long as the baby suckles in the first few days and keeps doing it, it will produce milk.

Uterus shrinks down rapidly and goes back from being at the ribs down to the umbilicus. By 10 days, it would have disappeared down into the pelvis and will no longer be able to feel it in the abdomen. It never quite goes back.

After 6 weeks, pretty much everything goes back to normal.