REPRO: 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 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

Basal metabolic rate in pregnancy

Answer 3

rises by 350 kcal/day mid-gestation
rises by 250 kcal/day late-gestation

75% of this increase is for foetus and uterus, 25% for respiration

Question 4

Many changes occur during pregnancy.

What do these changes cope for?

Answer 4

The changes are designed to cope with several main events:

• 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 5

List the systems in which the changes occur.

Answer 5

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

Question 6

Which hormones cause most of the changes?

Answer 6

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 7

Where do the effects of placental steroids take place?

Answer 7

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

Question 8

Describe the distribution of weight gain during pregnancy.

Answer 8

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 9

How does our energy balance change during pregnancy?

Answer 9

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

Question 10

What are some requirements for glucose during pregnancy?

Answer 10

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 11

How is glucose stored and utilised in different trimesters of pregnancy?

Answer 11

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 12

Gestational diabetes

Answer 12

diabetes during pregnancy

-common in the 2nd trimester due to insulin resistance from hPL and oestrogen

Question 13

Where does all the water gain come from?

Answer 13

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 14

Effect of pregnancy on total water gain

Answer 14

oestrogen and progesterone affect the renin/angiotensin axis by causing:

• thirst (decreased thirst threshold)
• fluid retention
• sodium retention
• decrease in plasma oncotic pressure (albumin levels drop)
• resetting of osmostat
• total increase in plasma volume and this will be distributed to different areas
• very common for some of it to end up in oedema

Question 15

How do E2 and P increase oxygen consumption?

Answer 15

oestrogen & progesterone affect repiratory centre in the brain:

• increased sensitivity to CO2
• women breathe more deeply
• increase in minute volume by 40%
• therefore increase in arteriole PO2 (10%) and decrease in PCO2 (15-20%)
• The thoracic anatomy changes, with the ribcage displacing upwards and the ribs flaring outwards.

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

40-50% increase in plasma volume
20% increase in red blood cell mass

HAEMODILUTION
-more plasma serum and less red blood cells (apparent anaemia due to concentration of haemoglobin falling, not the amount)

• increase in white blood cells and clotting factors; blood becomes hypercoagulable. This means increased fibrinogen for placenta separation but also increasing risk of thrombosis
• To make all the additional red blood cells, there is increased efficiency of iron absorption in the gut.

Question 17

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

Answer 17

increased Hb with altered type (HbF)

• increased O2 affinity than maternal Hb (HbA)
• therefore oxygen given up by HbA to HbF

foetus has higher Hb concentration than mother

Question 18

How does smoking affect the foetus’s oxygen levels?

Answer 18

causes foetal hypoxia because more maternal carboxy-Hb, stopping the transfer of oxygen to the foetus because carboxy-Hb is more permanent

Question 19

What changes occur to the cardiovascular system during pregnancy?

Answer 19

Changes in ECG and heart sounds

• expanding uterus pushes the heart around
• murmurs develop due to high blood flow

Increased Cardiac Output

• increased heart rate and stroke volume
• for maternal muscle (uterus), skin, kidneys and foetal supply across the placenta
• begins as early as 3 weeks to max at 40% increase at 28 weeks

Blood Vessels
-lower blood pressure despite greater CO due to a greater reduction in TPR by vasodilation

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

How do steroids affect our 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

How does our urinary system change during pregnancy?

Answer 24

The urinary tract dilates and relaxes.

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 (uterus enlarges compressing the bladder)
Mid-pregnancy: more normal micturition (the uterus is lifted out of the pelvis and there is less pressure on the bladder)
Late pregnancy: more frequent micturition (foetus head compresses bladder and increases)

Question 26

Changes in uterine size during pregnancy

Answer 26

hypertrophy: huge increase in muscle mass
huge increase in blood flow

*placenta+uterus receive 1/6 of total blood supply (hence a lot of bleeding during C-section)

Question 27

Why are pregnant women more prone to UTIs?

Answer 27

due to urinary stasis from smooth muscle relaxation

it may persist after pregnancy

Question 28

Changes in the uterus during pregnancy

Answer 28

isthmus (lower part of the uterus) expands and is less muscular and more fibrous, forming the lower uterine segment, which acts as a funnel to allow the baby to come down

top of the uterus still muscular to push the baby down

Question 29

What changes occur to the cervix during pregnancy?

Answer 29

• increase in vascularity (to retain the pregnancy)
• connective tissue softens from 8 weeks to begin gradual preparation of the expansion
• proliferation of mucosal glands (mucus = half of the mass), greatly increasing mucosal production (protective, anti-infective)

Question 30

Where is the incision made during a C-section?

Answer 30

lower segment C-section because there is less bleeding when there is less muscle and more fibrous structures

Question 31

How does the body return back to normal after birth?

Answer 31

Returns to normal:

• dramatic & 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 and never return to pre-pregnancy size
• removal of steroids (oestrogen and progesterone) permits action of raised prolactin on the breast for breastfeeding

Question 31

Cervix during labour is softened by…

Answer 31

inflammatory mediators and prostaglandins