applied physiology pregnancy

Energy requirement

Increased basal metabolic needs

Fat deposits for lactation

Placental and maternal tissue

Foetal growth

Progesterone

Slows gut motility, smooth muscle relaxation → reduced gastrointestinal motility and increased nutrient absorption

Physiological changes in glucose metabolism

A diabetogenic state - to ensure an adequate glucose supply to growing foetus

First trimester: increased sensitivity to insulin = increase glycogen synthesis and fat deposition

Second trimester: insulin resistance - hormones cortisol, progesterone, oestrogen and human placental lactogen (HPL) are insulin antagonists = glucose levels may rise in blood glucose

Blood required

Placental development and uterus changes requires ~1 litre of blood

Blood volume must increase

How much does plasma and blood volume increase?

~30-40% by 34 weeks pregnancy - accounts for 8-10kg of 10-13kg weight gain during pregnancy

~20% increase in red cell colume

Increase in RBC, there is overall haemodilution

Increase plasma volume consequences

Associated with reduced colloid osmotic (oncotic) pressure

Causes a shift of fluid into extracellular space

Increased hydration of connective tissue

Oedema (lower limbs, hands and face)

Mechanism of increased plasma volume

RAAS: increased renin → ang II → aldosterone

Aldosterone promotes water retention in kidneys = increase extracellular fluid and plasma volume

Oxygen availability

Increased demand for O2 and plasma blood volume

Red cell mass increases by ~20%

Increased iron absorption from gut - iron required for increased red cell mass

Deliver blood to uterus → uterine artery blood flow increases 3.5 fold from 95 to 342 ml/min

White blood cells

Concetration doesnt fall

Total wbc increases

Neutrophils increased → reduce apoptosis

Marked increased around delivery

Cardiovascular adaptations

Increase blood volume (30-40%) - cardiac output 50% increase

Peripheral resistance decreases by 35% - from progesterone causing peripheral vasodilation

Bp is only a small change

Respiratory adaptations

Increased pulmonary blood flow - increase breathing rate and tidal volume → increased minute and alveolar ventilation

Decrease maternal pCO2 and increase maternal pO2

Increase availability of O2 to tissues aids passive diffusion at placenta i.e. higher o2 concentration gradient - reduction in maternal CO2 and O2 concentration elevation = o2 diffusion gradient across placenta → o2 transfer to foetus

Foetal haemoglobin changes

High blood flow maximises PO2 on maternal side of placenta

HbF (foetal haemoglobin) has higher affinity for O2 compared with maternal adult Hb (HbA)