10- Maternal Changes In Pregnancy

Question 1

Why is a pregnant female considered a very different physiological being compared to normal males and females?

Answer 1

There are major changes in multiple systems that occur in the body during pregnancy.
The causative factors are:
- 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.

Question 2

How is an abnormality in pregnancy diagnosed?

Answer 2

To diagnose abnormality in pregnancy need to detect changes in the changes!
However, pregnancy may:
- exacerbate a pre-existing condition
- uncover ‘hidden’ or mild condition

Question 3

What events are maternal changes designed to cope with?

Answer 3

• 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
• preparation for delivery and puerperium

Question 4

In what systems do these maternal changes occur?

Answer 4

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

Question 5

Which hormones cause most of the changes that occur during pregnancy?

Answer 5

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

Question 6

Where do the effects of placental steroids take place?

Answer 6

• renin/angiotensin system
• respiratory centre
• GI tract
• blood vessels
• uterine myometrial contractility

Question 7

Describe the distribution of weight gain during pregnancy.

Answer 7

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.

Question 8

What changes occur in energy balance during pregnancy?

Answer 8

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

Question 9

What are the requirements for glucose during pregnancy?

Answer 9

The need for glucose is increased in availability in 2nd trimester
- active transport across placenta as fetal energy source
- fetus stores some in liver

Question 10

How is glucose stored and utilised in the first trimester?

Answer 10

Used in maternal reserves
- pancreatic beta cells increase in number
- plasma insulin increases
- fasting serum glucose decreases
(laid down as stores and used by muscle)

Question 11

How is glucose stored and utilised in the 2nd trimester?

Answer 11

Used in fetal reserves
- hPL causes insulin resistance - less glucose into stores leads to increased availability in serum
- glucose (more crosses placenta) but can cause diabetes

Question 12

Where does all the water gain come from during pregnancy?

Answer 12

The water gain during pregnancy can account for up to 8.51 litres, coming from:
- foetus
- placenta
- amniotic fluid
- oedema (lungs, connective tissue, ligaments, leakage, swollen ankles)
- uterine muscles
- mammary glands
- plasma volume

Question 13

How is plasma volume increased during pregnancy?

Answer 13

• sodium retention
• resetting of the osmostat
• decreased thirst threshold
• decrease in plasma oncotic pressure (albumin)

(E2 and P act on the renin-angiotensin system)

Question 14

What changes occur in respiration during pregnancy?

Answer 14

increased oxygen consumption

Question 15

What are the effects of E2 and P on the respiratory system?

Answer 15

E2 and P work together to increase oxygen consumption
They do this by increasing 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.

Question 16

How does maternal blood composition differ from normal blood composition, and what effect does that have?

Answer 16

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.

Question 17

How is the foetal blood able to take oxygen off of the mother’s blood?

Answer 17

Foetal blood has increased haemoglobin and an increased type, that has a high affinity for oxygen. This increases O2 binding.
Thus, oxygen is given up by the maternal Hb.

Question 18

How does smoking affect the foetus’s oxygen levels?

Answer 18

Smoking increases maternal carboxy-Hb which is more permanent and reduces the increasing binding, leading to foetal hypoxia.

Question 19

What changes occur in the cardiovascular system during pregnancy and what are the causes of these changes?

Answer 19

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

Question 20

If the stroke volume increases during pregnancy, how do we get decreased blood pressure?

Answer 20

Due to increased cardiac output and vasodilation by steroids, there is a reduced peripheral resistance.

This gives us a decrease in blood pressure overall.

Question 21

Where does the increased blood flow go to?

Answer 21

• uterus
• kidney
• placenta
• muscle
• skin

also, neoangiogenesis, including the extra capillaries in the skin (spider naevi) to assist in heat loss

Question 22

What are the effects of maternal steroids on the GI tract?

Answer 22

They:
- increase out appetite and thirst
- reduce GI motility (leading to constipation)
- relax the lower oesophageal sphincter (leading to acid reflux)

The increase in uterus size also contributes to the acid reflux, along with making the mother eat small frequent meals.

Question 23

What is the significance of folic acid in pregnancy?

Answer 23

It is involved in DNA production, growth and blood cells. These go on to the uterus, placenta and foetus.

Supplementation is advised, about 5 mg/day up to week 12.
A deficiency in folic acid is linked to spina bifida - a neural tube defect.

Question 24

What changes occur in the urinary system during pregnancy?

Answer 24

The urinary tract dilates and relaxes, which may lead to increased UTIs, and it may persist after pregnancy.

The kidneys get an increased blood flow, which leads to an increased filtration rate, and thus an increased clearance of:
- creatinine
- urea
- uric acid

Question 25

How does the frequency of micturition change during pregnancy?

Answer 25

Early pregnancy: more frequent micturition
Mid-pregnancy: more normal micturition
Late pregnancy: more frequent micturition

Question 26

What changes occur in uterine size during pregnancy?

Answer 26

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

Question 27

What changes occur in the cervix during pregnancy?

Answer 27

Its primary function of the cervix is to retain the pregnancy, for eg. by increasing the vascularity.

The tissue softens from 8 weeks. There are changes in connective tissue (starts to break down) as it starts the gradual preparation for expansion.

There is also a proliferation of the glands, which leads to the mucosal layer becoming half of the mass. There is a great increase in mucus production, which has protective and anti-infective purposes.

Question 28

When are the changes that occur during pregnancy reversed and what causes this reversal?

Answer 28

There is a dramatic and rapid fall in steroids on the delivery of the placenta. Most endocrine-driven changes then return to normal rapidly.
The removal of steroids permits the action of raised prolactin on the breast.

The uterine muscles rapidly loses oedema, but it contracts slowly: it will never return to pre-pregnancy size.