Pituitary hormones

• FSH/LH fall to extremely low levels due to the high levels of oestrogen and progesterone.
• Prolactin levels increase.
• Pituitary growth hormone (GH) levels fall but overall serum levels increase due to placental production.

Thyroid and parathyroid gland

• Thyroxine-binding globulin (TBG) concentrations rise due to increased oestrogen levels.
• T4 and T3 increase over the first half of pregnancy but there is a normal to slightly decreased amount of free hormone due to increased TBG-binding. Normal ranges are slightly reduced in the second and third trimester.
• TSH production is stimulated after the first trimester, although in healthy individuals this is not usually significant. A large rise in TSH is likely to indicate iodine deficiency or subclinical hypothyroidism.

Adrenal gland and pancreas

• Cortisol levels increase in pregnancy, which favours lipogenesis and fat storage.
• Insulin response also increases so blood sugar should remain normal or low.
• Peripheral insulin resistance increases after early stages of pregnancy due to increased production of hormones such as cortisol, prolactin, progesterone and human placental lactogen.

Blood:

• Plasma volume – Increased
• Red Blood Cells – Increased

Cardiovascular

• Peripheral vasodilation and decrease systemic vascular resistance
• Increased cardiac output (increased stroke volume and increased heart rate)
• Increased circulatory volume (increased plasma volume)
• Blood Pressure reduced in the 2^nd trimester
• Shortened PR and QT interval
• Ejection systolic murmur
• Shifted QRS axis to the left in the 3^rd trimester

Respiratory:

• Increased minute ventilation (increased tidal volume)
• Increased oxygen consumption
• State of compensated respiratory alkalosis – arterial pCO₂ drops, arterial pO₂ rises and decrease in bicarbonate prevents pH change.
• Tidal volume increases by about 200 ml, increasing vital capacity and decreasing residual volume.
• In later stages of pregnancy, splinting of the diaphragm may occur with some decrease in tidal volume.

Renal: –

• Glomerular filtration rate increases (50%) by end of first trimester
• Functional capacity of kidneys increase
• Ureters and renal pelvis dilate