Maternity

Pregnancy produces coordinated changes across nearly every maternal organ system. These changes support placental perfusion, fetal growth, and the increased work of labour, but they also alter what counts as expected. Plasma volume expands more than red-cell mass, creating the dilutional anaemia of pregnancy. Cardiac output rises through increased heart rate and stroke volume, while systemic vascular resistance falls because of progesterone-related smooth-muscle relaxation and the low-resistance uteroplacental circulation. The renin–angiotensin–aldosterone system supports sodium and water retention during this expansion. A mildly increased heart rate or exertional breathlessness may therefore be physiological; sudden dyspnoea, chest pain, syncope, cyanosis, or unilateral leg swelling is not explained by normal adaptation and requires urgent assessment. The enlarging uterus can compress the inferior vena cava when the patient lies flat, reducing venous return and potentially reducing uteroplacental perfusion. If dizziness, pallor, nausea, hypotension, or a concerning fetal heart-rate pattern develops in the supine position, turn the patient to a lateral position—usually left lateral—and reassess. Position is a treatment for the mechanism, not merely a comfort measure. Human chorionic gonadotropin, produced by the syncytiotrophoblast, maintains...