Physiological Changes in Pregnancy

Increased availability of precursors for hormone production and fetal-placental metabolism ; Improved transport capacity ; Maternal-fetal exchange ; and removal of additional waste products

Volume homeostasis

Factors contributing to fluid retention ↑Sodium retention Factors contributing to fluid retention ↑Sodium retention . Resetting of osmostat . ↓ Thirst threshold . ↓ Plasma oncotic pressure . Consequences of fluid retention ↓ Haemoglobin concentration . ↓ Haematocrit . ↓ Serum albumin concentration . ↑ Stroke volume

Haemostasis and Coagulation Increases in : Erythrocyte sedimentation rate ; Fibrinogen concentration ; 50 % ( 450 mg/dL ) . Activated protein C resistance ; Factors VII , VIII , IX , X and XII ; D-dimers ; Alkaline phosphatase . Von-willebrand factor . Antithrombin III unchanged plasminogen – activator inhibitor ( PAI – 1 , 2 )

Decreases in : Haemoglobin concentration . Haematocrot . Plasma folate concentration . Protein S activity . Plasma protein concentration , particularly albumin . Creatinine , urea , uric acid

The immune response : reduced numbers of cytotoxic ( CD8+ ) T cells during pregnancy , with potentially harmful T cell-mediated immune responses downregulated . The total white cell count increases up to values of 14 x 109/L in the third trimester . Counts of B cells appear to be unaltered numbers of natural killer ( NK ) cells increase in early pregnancy and decrease in late gestation .

Respiratory tract Ventilatory Changes: nasal congestion &rhinitis Thoracic anatomy changes . ↑ Minute ventilation . ↑ Tidal volume . ↓ Residual volume . ↓ Functional residual capacity . Vital capacity unchanged or slightly increased . Pulmonary blood flow increased .

Blood gas and acid-base changes ↓PCo2 ↑ PO2 pH alters little . Bicarbonate excretion increased . ↑ Oxygen availability to tissues and placenta . ↑ O2 consumption by 45 ml/min . Shifts of O2 – Hb dissociation curve to the right

Cardiovascular system Elevation of the diaphragm , adjustments of lung volumes and increases in minute ventilation give rise to breathlessness . Oedema in the extremities is a common finding . Sinus tachycardia . Premature atrial and ventricular ectopic beats are common in pregnancy . Cardiac output increases

Decreases in diastolic blood pressure ( 10 – 15 mmHg ) are more marked during antenatal period than the decrease in systolic pressure ( 5 – 10 mmHg ) . A 70 per cent reduction in peripheral resistance has been demonstrated by 8 weeks gestation . At delivery , a shift of blood from the empty uterus into the maternal circulation – called autotransfusion .

The first heart sound is loud . While a third heart sound is aubible in 84 per cent of pregnant women by 20 weeks gestation . An ejection systolic murmur can be heard .

Cardiovascular changes Heart rate ( 10 – 20 per cent ) . Stroke volume ( 10 per cent ) . Cardiac output ( 30 – 50 per cent ) 7 L / min . Mean arterial pressure ( 10 per cent ) . Pulse pressure . Peripheral resistance ( 35 per cent ) .

Gastrointestinal changes Pregnancy gingivitis . Increased tooth mobility . Elevated progesterone levels reduce lower oesophageal sphincter tone and increase the placental production of gastrin , increasing gastric acidity . The enlarging uterus and progesterone levels all contribute to delayed gastric emptying . Constipation .

kidneys and urinary tract Kidney size ( 1 cm ) . Dilatation of renal pelvis and ureters . ↑ Blood flow ( 60 – 75 per cent ) . ↑ Glomerular filtration ( 50 per cent ) . ↑ Renal plasma flow ( 50 – 80 per cent ) . ↑ Clearance of most substances : ca , protein . ↓ Plasma creatinine , urea and urate . Glycosuria is normal . K+ Metabolism unchanged .