Lecture 15: Maternal physiology

Question 1

Why does the body need to adapt in pregnancy?

Answer 1

Increased waste clearance: increased GFR and hepatocellular stimulation
Nutrition: increased respiration, increased absorption, insulin resistance
Childbirth: changes in clotting factors and MSK structures

Question 2

What drives the adaptations during pregnancy?

Answer 2

Hormones

• hCG
• oestrogen
• progesterone
• relaxin
• hPL (human placental lactogen)

Question 3

What is the role of relaxin?

Answer 3

• softening ligaments

- widens the cervix

Question 4

Why does immunity change during pregnancy?

Answer 4

Because we want the baby to thrive and the mother to be a good host
-usually mother would reject the baby due to immune reaction
(achieved by immune regulation)

Question 5

What are the adaptations within the immune system in pregnancy?

Answer 5

Fetus
-recognised by maternal immune system
-incited allo-response is not cytotoxic
Mother
-in pregnancy undergoes an immunosuppressed state (placental progesterone, upregulation of HLA and therefore IL10 which drives tolerance through Th2 (not cytotoxic) cells, which downregulates Th1 cytotoxic cells)
-may improve certain autoimmune conditions
-higher attack rate and severity of certain viral pathogens (e.g. varicella-chicken pox)
=overall no cytotoxic response but baby is recognised

Question 6

How is respiration changed during pregnancy?

Answer 6

Increased ventilation
-baby needs oxygen delivery and carbon dioxide removal
-mum needs continued oxygen delivery to her organs and periphery
=increased oxygen supply to meet metabolic demand and increased carbon dioxide clearance

• TV increased by 30-40% (chest diameter can increase in pregnant women)
• ERV decreased by 20%
• increased minute ventilation by 40-50% (increased oxygen levels, decrease in carbon dioxide- could lead to pH change)
• TLC decreased by 5%: at term, the child pushes against the diaphragm

Progesterone relaxes smooth muscle in the airways reducing airway resistance

Question 7

Why do you commonly see dyspnoea in pregnancy?

Answer 7

Occurs in 60-70% of patients

• multifactorial
• most likely due to hyperventilation
• need to consider pathological causes/exacerbating factors

Question 8

What are the changes to the cardiovascular system and haematology during pregnancy?

Answer 8

-baby needs delivery of nutrients
-mum needs to fill utero-placental-fetal circualtion, oxygenate growing uterus (very vascular-high demand), prepare for potential blood loss during delivery, protect from any impairment of venous return
Achieved by
=volume expansion
=clotting mechanisms

Question 9

How is volume expansion of blood achieved during pregnancy?

Answer 9

Increased CO
-early: increased stroke volume
-late: increased HR (no more than 95 bpm)
Progesterone: smooth muscle relaxation, decreasing systemic vascular resistance and a drop in BP
-oestrogen and progesterone act on kidney to active RAAS, and oestogren acts on liver to produce angiotensinogen, this usually causes vasoconstriction but in pregnancy it doesn’t (probably due to smooth muscle relaxation), it still causes release of aldosterone from adrenal gland which acts on the kidneys to stimulate reabsorption of salt and water therfore increasing the SV

Question 10

What are the clotting mechanisms in pregnancy?

Answer 10

• increased procoagulants (fibrinogen. factor 8, vWF)
• decreased anticoagulants (protein S)
• reduced fibrinolysis

Question 11

What consequences do we see due to changes to the CVS in pregnancy?

Answer 11

Increased RAAS: peripheral oedema
Change in plasma volume> change in RBC volume: dilutional anaemia
Hypercoagulable state: increased number of thromboembolitic events

Question 12

What are the changes to the renal system during pregnancy?

Answer 12

-baby needs to remove waste
-mum needs to increase the clearance of waste
Acheived by
=increased GFR by 50% (therefore you see decreased serum urea and creatinine by 25%)
Systemic vasodilation- increased renal blood flow causing increased GFR
Decreased PCT reabsorption
Smooth muscle relaxation (progesterone): increased size of kidneys and ureters, decreased speed of urine passage

Question 13

Why may you see glucosuria in pregnant women?

Answer 13

Due to decreased PCT reabsorption, because of increased filtrate rate and blood flow

Question 14

Why do you get more UTI’s in pregnancy?

Answer 14

Due to decreased speed of urine passage

Question 15

What is the overall change to the GI system in pregnancy?

Answer 15

Slower transit time

• baby needs nutrients
• mother needs to feed herself and the baby
• increased absorption of minerals and vitamins

Question 16

What are the adaptations to the GI tract in pregnancy?

Answer 16

Progesterone causes:

• decreased small and large bowel motility to increase mineral and water absorption: constipation
• decreased lower oesophageal sphincter tone: GORD
• decreased gallbladder contractility: gallstones

(uterus is retroflexed so this displaces the bowel which can cause mechanical obstruction)

Question 17

Are LFT’s affected by pregnancy?

Answer 17

ALP levels increased due to placental synthesis

Question 18

What are the adaptations of the thyroid during pregnancy?

Answer 18

Fetal dependency on maternal thyroxine up to around 12 weeks

• oestrogen stimulates TBG hepatic production (thyroxine binding globulin)
• need to increase thyroxine production so we get free thyroxine, as we need free thyroxine to avoid binding of TBG to provide the fetus
• hCG has a similar alpha-subunit to TSH so stimulates the thyroid

Question 19

What is the adaptation to PTH and calcium?

Answer 19

Calcium is required for development of baby’s bones
-Ca2+ reduces due to baby using it
-this stimulates the parathyroid glands to increase PTH, causing increased 25(OH)D (intermediate of vit D), placenta causes increased 1-alpha-hydroxylase which converts 25(OH)D to 1,25(OH)2D (active form of vit D)
=increased Ca2+ and phosphorus absorption in gut (maintain equilibrium of calcium, so we don’t see changes to mums bones to accomodate)

Question 20

How does glucose metabolism change during pregnancy?

Answer 20

Insulin resistance: increase glucose levels, allowing glucose for fetus (due to constant hyperglycaemia allowing for glucose flux)
=diabetogenic pregnancy

Question 21

What hormones cause insulin resistance?

Answer 21

• tumour necrosis factor alpha
• human placental lactogen
• placental growth hormone
• oestrogen
• cortisol
• progesterone

Question 22

What is gestational diabetes mellitus?

Answer 22

Onset of elevated blood sugar levels during pregnancy

Increased insulin resistance so more glucose going to baby (due to obesity/physical inactivity/ethnicity/PCOS)
-increase in glucose flux
-defective insulin secretion, can’t secrete enough
-enhanced size of fetal growth: issues with delivery
Results in increased risk of diabetes later in life

Question 23

What is the increase in weight with a pregnancy?

Answer 23

11-15kg

Question 24

What are the adaptations in MSK during pregnancy?

Answer 24

Change in centre of gravity
-increased lordosis and kyphosis 
-forward flexion of neck
Stretching of abdominal muscles 
-impede posture
-strain paraspinal muscles
=back pain, shoulder pain, tension headaches

-increased mobility of sacroiliac joints and pubic synphysis
-anterior tilt of pelvis
=pelvic pain

Fluid retention (due to increased volume in circulatory system) can compress structures such as median nerve e.g. carpal tunnel

Question 25

What are the adaptations in skin during pregnancy?

Answer 25

• spider angioma, palmar erythema due to oestrogen increase

- increase in melanocytic stimulating hormone: hyperpigmentation (linea nigra)

Question 26

What is preeclampsia?

Answer 26

Hypertension and proteinuria

• usually presents in the third trimester
• multisystem disorder
• impaired invasion of the trophoblast leading to shallow invasion of spiral arteries
• leads to hypoperfusion and ischaemia
• this also causes systemic endothelial dysfunction in mum

Question 27

What are some risk factors of preeclampsia?

Answer 27

• diabetes
• obesity
• FHx
• chronic/gestational hypertension
• renal disease
• first pregnancy
• extremes of age
• IVF
• preeclampsia in prior pregnancy

Question 28

What are the complications of preeclampsia?

Answer 28

Maternal (vasoconstriction due to systemic endothelial dysfunction)

• seizure (eclampsia): serious
• cerebral haemorrhage
• renal failure
• pulmonary oedema
• DIC and thrombocytopenia
• hepatic failure

Fetal

• growth restriction
• fetal distress
• stillbirth
• placental infarction
• premature delivery
• oligohydramnios (reduced amniotic fluid)

Question 29

When is hCG detectable in urine/serum?

Answer 29

Urine: 14 days after fertilisation
Serum: 7 days after fertilisation

Question 30

Can tubal pregnancies always be diagnosed by USS?

Answer 30

No

Question 31

What is placenta accreta and placenta percreta?

Answer 31

Placenta accreta: fertilised ovum invades beyond the endometrium into the myometrium
Placenta percreta: fertilised ovum ivades full width of uterus

Question 32

Why is fat laid down in the first half of pregnancy?

Answer 32

Helps mother meet the demands of the fetus later on in the pregnancy when the fetus is most demanding
-progesterone also increases appetite in the first half of pregnancy and diverts glucose into fat synthesis

Question 33

Why may you get flow mumurs and upwards displacement of the apex beat during pregnancy?

Answer 33

Due to increased plasma volume

Question 34

What hormones stimulate breast growth?

Answer 34

• oestrogen
• progesterone
• prolactin

Question 35

How do you manage eclampsia?

Answer 35

Deliver the baby and the placenta