In one line
Maternal sepsis is life-threatening organ dysfunction caused by a dysregulated host response to infection in pregnancy, labour, the puerperium or after abortion; the mother who dies is almost always the one in whom the diagnosis was made late, because the physiology of pregnancy hides the early signs — and survival turns on two things done within the first hour, broad-spectrum antibiotics and a relentless hunt for the source to control.
Mechanism & pathophysiology
Sepsis is not severe infection and it is not bacteraemia. The Sepsis-3 consensus reframed it as life-threatening organ dysfunction due to a dysregulated host response to infection — the lethal element is the host response, not the organism. An invading pathogen, recognised through pattern-recognition receptors, triggers a coordinated release of pro-inflammatory cytokines (TNF-α, IL-1, IL-6) that is appropriate when local and catastrophic when systemic. The endothelium is the organ that fails first and worst: glycocalyx shedding, loss of barrier integrity and widespread microvascular leak produce the clinical triad of vasoplegia, maldistribution of flow and capillary leak. Nitric-oxide-driven vasodilatation drops systemic vascular resistance; arterial and venous tone collapse; fluid escapes the intravascular space. The result is a paradox — a patient who is volume-deplete intravascularly yet oedematous, with tissue hypoperfusion despite a normal or high cardiac output. Mitochondrial dysfunction means oxygen that does reach the cell cannot be used; lactate rises as a marker of that cellular distress, not simply of anaerobic debt. Coagulation is activated in parallel, consuming platelets and clotting factors and producing the microthrombi of disseminated intravascular coagulation that occlude the very capillaries already starved by maldistribution.
The immune derangement is not a simple cytokine storm but a two-phase dysregulation, and the distinction has bedside consequences. The early hyperinflammatory phase is followed — sometimes overlapping — by a compensatory anti-inflammatory and immunoparalytic state, in which monocyte HLA-DR expression falls, lymphocytes are lost to apoptosis, and the patient becomes susceptible to secondary and nosocomial infection. This is why a septic mother who appears to turn the corner can deteriorate again days later from a new organism, and why immunosuppression — including HIV — compounds an already maladaptive host response. The complement and contact pathways are activated alongside cytokines, generating the anaphylatoxins that amplify vasodilatation and capillary leak. Tissue factor exposed on damaged endothelium initiates coagulation, while the natural anticoagulant systems (protein C, antithrombin, tissue-factor-pathway inhibitor) are consumed and downregulated; the net pro-thrombotic shift, uncoupled from effective anticoagulation, is the molecular basis of the DIC that clinically presents as bleeding from puncture sites alongside microvascular thrombosis. Understanding that coagulation and inflammation are the same dysregulated process is what makes the failure of activated protein C as a therapy intelligible — restoring one node of a system-wide collapse was never going to rescue the whole.
Septic shock is the subset in which these circulatory, cellular and metabolic derangements are profound enough to carry a substantially higher mortality — operationally, a patient who needs a vasopressor to hold a mean arterial pressure of 65 mmHg and has a lactate above 2 mmol/L despite adequate fluid resuscitation. That two-part definition matters: a low blood pressure that corrects with fluid is not septic shock, and a persistently raised lactate after resuscitation signals shock even when the pressure has been propped up. The lactate deserves a mechanistic caveat the consultant should be able to defend: in sepsis it is only partly a marker of anaerobic, hypoperfusion-driven metabolism — adrenergic stimulation of aerobic glycolysis and impaired hepatic clearance both contribute — so a raised lactate is a marker of severity and a target for clearance, not a literal oxygen-debt gauge to be chased with fluid alone.
Pregnancy is the reason this presents late and progresses fast. The adaptive physiology of a normal pregnancy is, point for point, a near-perfect camouflage for early sepsis. Resting heart rate is already raised by 10–20 beats per minute, so a compensatory tachycardia looks like pregnancy. Systemic vascular resistance and blood pressure are physiologically lower, so the relative hypotension that should alarm reads as normal for a gravid woman. The white cell count is elevated in healthy pregnancy and rises further in labour, so leucocytosis loses its discriminatory value. Tidal volume and minute ventilation are already high, so a rising respiratory rate — the single most sensitive early sign of deterioration — is easily dismissed. The gravid uterus splints the diaphragm and shifts abdominal landmarks, blurring peritoneal signs. Onto this baseline the mother brings a relatively immunotolerant state that permits the fetus and, in doing so, blunts containment of infection. The net effect is a wider, faster trajectory from infection to organ failure on a background that disguises every early warning. The young, previously fit obstetric patient also compensates impressively — until she does not, decompensating precipitously from what looked like a stable picture an hour earlier.
The sources cluster by timing and anatomy. Chorioamnionitis in the antenatal and intrapartum period, ascending from the genital tract, often with prolonged rupture of membranes. Endometritis is the dominant puerperal source — retained products and an open, devascularised placental bed make the postpartum uterus a culture medium, and it is the commonest infective focus after both vaginal and caesarean delivery. Septic abortion, whether after unsafe termination or incomplete miscarriage, drives some of the most fulminant disease, with retained tissue as an uncontrolled source. Beyond the genital tract sit the non-obstetric sources that kill exactly because they are not looked for: pyelonephritis (pregnancy's ureteric dilatation and stasis make ascending urinary infection common and severe), pneumonia and influenza (to which pregnant women are unusually susceptible and from which they deteriorate quickly), wound and episiotomy infection including necrotising soft-tissue infection, and mastitis progressing to breast abscess. The organism that disproportionately kills is group A streptococcus (Streptococcus pyogenes): it produces superantigen-driven toxic shock, necrotising endomyometritis and fasciitis, and a deceptively well-looking woman can be peri-arrest within hours; it is the single most frequent organism in fatal maternal sepsis, often community-acquired from a child with a sore throat. Escherichia coli and other Gram-negatives dominate urinary and genital sources; polymicrobial pictures are common in retained-tissue and abscess disease.
South Africa adds its own drivers, and they reshape the differential. HIV is the dominant modifier — both a direct cause of overwhelming opportunistic infection and a state that worsens the course and completion of treatment of any sepsis. Disseminated tuberculosis is a specifically South African trap: it presents as an indolent, then suddenly fulminant, septic picture, is frequently extrapulmonary in HIV co-infection, and is missed when the team is anchored on a genital-tract source. Influenza and bacterial pneumonia carry disproportionate mortality. The implication is concrete: in this population a septic mother without an obvious genital source is TB or HIV-related sepsis until proven otherwise, and the HIV status is part of the assessment, not an afterthought.
The Saving Mothers confidential enquiries make the epidemiology unambiguous for SA practice: non-pregnancy-related infection — overwhelmingly AIDS-related — has been the leading cause of maternal death since 1999, and pregnancy-related sepsis sits among the top direct causes alongside hypertension and haemorrhage. The maternal mortality ratio in HIV-infected women runs roughly an order of magnitude above that in uninfected women, and the great majority of NPRI deaths occur in HIV-positive women. The advanced-HIV mother does not mount the febrile, leucocytotic response that flags sepsis in the immunocompetent; she may present with a normal temperature and a normal white count while disseminated TB, cryptococcal disease, pneumocystis or bacterial pneumonia smoulders. A blunted inflammatory response in an unwell, low-CD4 mother is therefore a reason for more concern, not reassurance — the absence of the classic signature reflects an immune system too depleted to produce it.