Maternal changes in pregnancy

Question 1

What are the causative factors of pregnancy?

Answer 1

• 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 would we diagnose an abnormality in pregnancy?

Answer 2

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

Question 3

What do the changes that occur during pregnancy cope for?

Answer 3

• 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

Question 4

List the systems in which the changes can occur

Answer 4

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

Question 5

Which hormones cause most of the changes?

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 (RAAS)
• respiratory centre
• GI tract
• blood vessels
• uterine myometrial contractility

Question 7

Summarise the weight gain that occurs 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

How does energy balance change 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 some requirements for glucose during pregnancy?

Answer 9

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

Question 10

How is glucose stored and utilised during pregnancy?

Answer 10

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)

Question 11

Where does all water gain come from?

Answer 11

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

Question 12

How do we increase the plasma volume during pregnancy?

Answer 12

• 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 13

How do E2 and P increase O2 consumption?

Answer 13

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.

Question 14

How does maternal blood composition differ from normal composition?

Answer 14

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 15

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

Answer 15

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

Question 16

What does smoking do to the foetus’s oxygen levels?

Answer 16

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

Question 17

What changes occur to the cardiovascular system during pregnancy?

Answer 17

Expanding uterus:

• pushes the heart around
• changes ECG and heart sounds

Increased cardiac output:

• increased heart rate and stroke volume
• begins as early as 3 weeks to max at 40% increase at 28 weeks
• for maternal muscle and foetal supply

Question 18

If the stroke volume increases during pregnancy, why does blood pressure decrease?

Answer 18

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 19

Where does the increased blood flow go to?

Answer 19

• uterus
• kidney
• placenta
• muscle
• skin

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

Question 20

How do steroids affect the GI tract?

Answer 20

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 21

What is the significance of folic acid in pregnancy?

Answer 21

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 22

What happens to the urinary system during pregnancy?

Answer 22

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 23

How does the frequency of micturition change during pregnancy?

Answer 23

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

Question 24

What changes occur to the cervix during pregnancy?

Answer 24

Its primary function 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 mucus becoming half of the mass. There is a great increase in mucus production, which has protective and anti-infective purposes.

Question 25

What happens to the body post birth?

Answer 25

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.