In one line
Pregnancy changes the meaning of almost every measurement you take, so a woman with a medical disorder can be seriously ill while every number on her chart looks acceptable. This chapter gives the physiology that resets those numbers, the pattern of avoidable death in South Africa, and a route into the detailed chapter for each condition.
Why this is where women die
The Saving Mothers reports of the National Committee for Confidential Enquiry into Maternal Deaths return to the same findings across triennia. Non-pregnancy-related infection, dominated by HIV and its sequelae of pneumonia and tuberculosis, sits alongside obstetric haemorrhage and hypertension at the top of the list, and medical and surgical disorders make up a substantial and largely avoidable fraction.
The avoidable factors recur so consistently that they are worth learning as a list in their own right:
- Late presentation by the woman, often for reasons of transport and cost rather than choice.
- Failure to recognise the sick pregnant woman, because her physiology compensates until it does not.
- Delayed referral up the levels of care, from clinic to district to regional to tertiary.
- Substandard monitoring, particularly of the respiratory rate, which is the single most predictive observation and the one least often recorded.
Everything else in this domain is downstream of those four.
The physiology that resets every reading
This is the part that only an overview can teach, because it applies to all of the conditions at once. A pregnant woman's normal range is not a non-pregnant woman's normal range, and treating a physiological adaptation as pathology, or a pathological value as physiological, is the commonest error in this whole domain.
| Adaptation | Magnitude | What it changes |
|---|---|---|
| Plasma volume rises more than red cell mass | Plasma up about 40–50% | A dilutional fall in haemoglobin, so pregnancy needs its own anaemia threshold. See [[anaemia-in-pregnancy]] |
| Cardiac output rises | About 30–50% | Resting tachycardia is normal, so tachycardia loses its value as an early alarm |
| Progesterone-driven hyperventilation | Minute ventilation up 30–50%; PaCO₂ falls to about 3.7–4.3 kPa; bicarbonate falls to about 18–22 mmol/L | A normal-looking PaCO₂ signals impending respiratory failure, and the low bicarbonate means less buffering reserve for any metabolic acidosis. See [[arterial-blood-gas]] and [[asthma-in-pregnancy]] |
| Functional residual capacity falls about 20% while oxygen consumption rises 20–30% | She desaturates far faster than a non-pregnant woman | |
| Hypercoagulability | Factors VII, VIII, X and XII and fibrinogen rise; free protein S falls; acquired activated protein C resistance; PAI-1 and PAI-2 rise | Virchow's triad is satisfied on all three limbs. See [[venous-thromboembolism-in-pregnancy]] |
| Renal plasma flow and GFR rise | GFR up about 50% | Normal creatinine and urea are lower, so a "normal" creatinine may be renal impairment; renally cleared drugs need higher doses |
| Ureteric dilatation and glycosuria | Right more than left | Ascending infection is easier and better fed. See [[urinary-tract-infection-in-pregnancy]] |
| Insulin resistance rises | Insulin sensitivity falls about 50% by the third trimester, with a two- to three-fold compensatory rise in insulin secretion | Gestational diabetes is the failure of that compensation. See [[diabetes-in-pregnancy]] |
| Thyroxine-binding globulin rises with oestrogen; hCG stimulates the TSH receptor | Total T4 and T3 rise about 50% | Total thyroid hormone measurements become uninterpretable, and a low first-trimester TSH is often physiological. See [[thyroid-disorders-in-pregnancy]] |
Four consequences follow from that table, and they are the operating rules of this domain:
- Tachycardia and breathlessness are unreliable alarms. The respiratory rate is the one that still works. Record it.
- A result inside the non-pregnant reference range may be abnormal. PaCO₂, creatinine, urea and bicarbonate all run lower in pregnancy.
- A result outside the non-pregnant range may be normal. Total T4, white cell count, alkaline phosphatase and D-dimer all run higher.
- She has less reserve than she looks. Less oxygen stored, less bicarbonate to spare, less time before decompensation.