18. Physiology of Pregnancy

Question 1

demands of the foetus

Answer 1

nutrients (O2, amino acids, glucose)
amniotic fluid production
removal of foetal waste products (CO2, nitrogen compounds)

Question 2

plasma volume

Answer 2

increases by 40%
2.5 to 3.7 litre by end of pregnancy 
11-13kg weight gain 
~1 litre is contained within maternal blood spaces of the placenta
\+prepares for blood loss during birth

Question 3

plasma colloid osmotic pressure

Answer 3

falls
causes shift of fluid into extracellular space
increased hydration of connective tissue
oedema (lower limbs, hands, face)

Question 4

how does plasma volume increase?

Answer 4

RAAS
oestrogen stimulates angiotensinogen secretion, eventually causing increased aldosterone secretion
+ progesterone stimulates aldosterone too
causes increased reabsorption of water and sodium

Question 5

effect of ANP

Answer 5

slight decrease
decreases thirst threshold (increases fluid intake)
osmostat is rest - plasma volume increases

Question 6

red blood cells in pregnancy

Answer 6

mass increases 25%
combats dilution anaemia caused by increased plasma volume
iron is required for increase in cell mass - more iron absorbed in gut and ferritin levels fall

Question 7

should iron be supplemented in pregnancy?

Answer 7

no, unless twins

ferritin levels and iron absorption in the gut increases to provide all necessary iron

Question 8

haemostasis

Answer 8

hypercoaguable state
increased: plasma fibrinogen, platelets, factor VII, von Willebrand factor
important during deliver: 500ml/min blood loss at placental separation

Question 9

uterine artery

Answer 9

blood flow increases 3.5 fold in pregnancy

95 to 345 ml/min

Question 10

white blood cells

Answer 10

concentration does not fall - total WBC increases
more neutrophils
around delivery = marked increase

Question 11

heart changes

Answer 11

enlarges by ~12%
innocent systolic murmurs (common, 90%)
diastolic murmurs - less common (20%) and require investigation
uterus pushing up against diaphragm may cause maternal heart to shift up in chest cavity

Question 12

diastolic murmurs

Answer 12

may be innocent
further investigation to to rule out cardiopathies
change in cardiac axis/position may result tinc changes on ECG and X ray

Question 13

peripheral resistance

Answer 13

peripheral vasodilation occurs due to progesterone

peripheral resistance is decreased by 35%

Question 14

blood pressure

Answer 14

decreased resistance is partly compensated for
cardiac output increases
small change is observed

Question 15

respiratory system

Answer 15

increased pulmonary blood flow is matched:
increased tidal flow
decrease in maternal pCO2 and increased maternal pO2
increased availability of O2 to tissues
- aids diffusion at placenta

Question 16

effects of CV and respiratory changes

Answer 16

high blood flow maximises O2 on maternal side of placenta
foetal haemoglobin has higher affinity for O2 than adult
increased CO may increase flow to skin: aids heat loss

Question 17

renal system

Answer 17

kidney increases 1cm in size
GFR and effective renal plasma flow increase by over 50%
tubular reabsorption capacity = unchanged- glucose reabsorption impaired
plasma creatinine and urea decrease
dilatation of renal pelvis and ureters (progesterone)

Question 18

GI system

Answer 18

gastro-oesophageal reflux - up to 70% - due to increased abdominal pressure
slowing of gut motility and constipation (progesterone)

Question 19

glucose metabolism in 1st trimester

Answer 19

increased sensitivity to insulin

increase glycogen synthesis and fat deposition

Question 20

second trimester

Answer 20

insulin resistance
cortisol, progesterone, HPL and oestrogen = insulin antagonists
glucose levels may rise
+ increase in fatty acids- energy sources for foetus

Question 21

folate importance

Answer 21

dan synthesis, repair and regulation
important for rapid cell division - embryos
deficiency in pregnancy associated with neural tube defects

Question 22

folate in pregnancy

Answer 22

daily requirement increased from 50mg to 400mg
significant tissue stores: dietary deficiency may take months to become apparent
no need for supplementation, but can precent neural tube defects

Question 23

thyroid funciton

Answer 23

increased iodine absorption 
increased serum T3 and T4 
increased TBG 
unbound T3 and T3 levels remain the same 
mostly remains unchanged

Question 24

hormones released by the placenta

Answer 24

protein
hCG - human chorionic gonadotrophin 
hPL - human placental lactogen 
hPG - human placenta gonadotrophin 
CRH - corticotrophin releasing hormone 
steroid 
progesterone 
oestrogen (oestradiol)

Question 25

human chorionic gonadotrophin (hCG)

Answer 25

first detectable 8-9 days after ovulation - peaks 8-10 week s
beta subunit used as pregnancy test
doubles every 48-72 hours
significantly lower in ectopic pregnancy + risk for miscarriage
alpha subunit = similar to LH, FSH, TSH
maintains corpus luteum secretion of progesterone and oestrogen
decreases as placental production progesterone increases

Question 26

human placenta lactogen (hPL)

Answer 26

secreted by placenta
responsible for regulating foetal growth
induces maternal insulin resistance

Question 27

placental corticotrophin-releasing hormone

Answer 27

stimulates production of maternal ACTH and cortisol

can result in increased maternal glucose

Question 28

progesterone

Answer 28

maintains uterine quiescence, decreases electrical activity
immune suppressor
lobule-alveolar development in breasts
substrate for foetal corticoid synthesis, e.g. cortisol

Question 29

oestrogen

Answer 29

growth of uterus, cervical changes
development of ductal system of breasts
stimulation prolactin synthesis, CBG, SHBG, TBH
90% as oestradiol