Reproductive Physiology

Cardiovascular system

• Cardiac output (CO) increases 30 to 50%

  • begins week 6

  • peaks between 16 and 28 weeks

  • may decrease slightly after 30 weeks due to obstruction of vena cava

  • increase by 30% more during labour

  • returns to normal by 6 weeks postpartum

  • blood flow to the uterus at term is about 1 L/min or 20% of normal CO

• Heart rate

  • increase in heart rate from 70 beats/min to 80 or 90 beats/min

• Blood pressure

  • BP falls in early pregnancy, nadir about week 22-24

  • may return to normal in 3rd trimester

  • BP directly proportional to systemic vascular resistance and cardiac output
  • Vasodilatation is primary change in pregnancy
  • May be low if woman supine due to diminished venous return
  • falls after delivery, then rises to peak 3-4 days later
    • ?return of normal vascular tone
    • ? vasomotor instability
• Murmurs may be heard, accentuated heart sounds
• Premature atrial and ventricular beats are common
• paroxysms of atrial tachycardia - may require digitalisation

Blood

• Blood volume increases proportionally with CO
  • increase in plasma volume is greater (close to 50%) than that in RBC mass (about 25%) leading to dilutional anaemia
• WBC increased slightly (to 9-12 x 10³ µL)_/ , markedly increased during labour and postpartum
• Iron requirements increased (about 1 g)

Urinary system

• Glomerular filtration rate (GFR) increased 30-50%

  • peak 16-24 weeks

  • blood urea and creatinine fall (urea <3.6 mmol /l, creatinine 62µmol/L)

• Ureters dilate due to progesterone / pressure due to enlarged uterus

• Positional increases in kidney function (so increases urine production when lying laterally/ asleep)

Respiratory system

• Due partly to progesterone partly to positional problems

• increase in

  • Tidal and minute volume

  • respiratory rate

  • plasma pH

  • O₂ consumption

• decrease in

  • Inspiratory and expiratory reserve,

  • residual volume and capacity

  • plasma PCO₂

• hyperaemia and oedema of the respiratory tract occur

  • nasopharyngeal obstruction and nasal stuffiness

  • Eustachian tubes are transiently blocked

  • tone / quality of voice change

• Mild dyspnoea during exertion

GI and hepatobiliary systems

• progesterone relaxes smooth muscle

  • decreased GI motility

  • Heartburn / belching

  • delayed gastric emptying

  • gastro-oesophageal reflux

• constipation

  • uterus pressing against the rectum and lower portion of the colon

• HCl production decreases

  • Peptic ulcer disease is uncommon

• Gallbladder disease increased

• alkaline phosphatase levels rise progressively during the 3rd trimester and may be 2 to 3 times normal at term (placental production)

Endocrine system

• protein binding increases

• increased thyroid function (placenta produces hormone similar to TSH)

  • tachycardia,

  • palpitations

  • excessive perspiration

  • emotional instability

  • enlarged thyroid gland

• Increased adrenal function

  • striae

  • oedema.

• Glucose metabolism altered

  • increased glucocorticoids, oestrogen, progesterone

  • increased insulin requirements

• melanocyte stimulating hormone - increases skin pigmentation

• hCG

  • functions like FSH/LH

  • maintains corpus luteum

  • prevents ovulation

Skin

• Melasma (mask of pregnancy)

  • forehead and malar eminences

• pigmentation of areolae

• linea nigra

  • mid-abdominal pigmentation

• spider naevi

• thin-walled, dilated capillaries in legs

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