In one line
Pregnancy hides tuberculosis and pneumonia while making both more dangerous, and the highest-risk period is not the pregnancy but the first months after delivery. Screen at every visit, treat with the standard regimens because they are safe, and remember that a woman who is breathless on the postnatal ward has less reserve than she looks like she has.
Where this sits. The organisms and the host response underneath this chapter are taught in the Primary chapter on microorganisms in pregnancy and the puerperium. The HIV layer that changes the presentation and the urgency is the Finals chapter on HIV in pregnancy, and the critically ill mother is obstetric critical care.
The infection that kills mothers without being written down
Non-pregnancy-related infection sits among the leading causes of maternal death in South Africa, and the largest part of it is respiratory. Globally, tuberculosis contributes to 6 to 15% of all maternal mortality. About 200 000 women develop tuberculosis in pregnancy or the puerperium each year, split as roughly 151 000 during pregnancy and 49 000 afterwards.
Look at how that 200 000 divides, because the split is stranger than it first appears. Pregnancy lasts nine months and the postpartum period, as counted here, lasts a few. Yet nearly a quarter of the cases fall in the shorter window. Expressed as risk rather than counts, the incidence risk ratio is 1.4 in pregnancy (95% CI 1.1 to 1.7) and 1.9 postpartum (95% CI 1.5 to 2.5).
So the dangerous period is after she has been discharged, when nobody is looking. That single observation reorganises how you think about the topic, and the reason for it explains almost everything else in this chapter.
Why a pregnancy tolerates a fetus, and what that costs her lungs
A fetus is, immunologically, half foreign tissue that the mother does not reject. Achieving that requires a real shift, not a vague dampening: maternal immunity moves away from cell-mediated, Th1-dominant responses and toward humoral, Th2-dominant ones, with expanded regulatory T-cell populations at the maternal-fetal interface.
That trade is excellent for the pregnancy. It is poor for anything the body controls with cell-mediated immunity.
Work out which infections that puts at risk and the list writes itself: the intracellular organisms. Tuberculosis is the obvious one, and the same logic covers listeria, and the fungal and viral infections that trouble immunosuppressed patients generally. This is the identical mechanism that makes pregnancy hard for a woman living with HIV, because her cell-mediated arm is already depleted, and the two deficits add (HIV in pregnancy).
Now run the mechanism forward past delivery. The tolerance was required for as long as there was a fetus. Once the placenta is delivered, that suppression lifts, and it lifts quickly.
A restored Th1 response meeting an infection that was quietly established during the tolerant months produces exactly what an immunologist would predict: inflammation appearing or worsening at the moment immunity returns. That is why the postpartum risk ratio is higher than the antenatal one, and it is the same phenomenon as immune reconstitution after starting antiretroviral therapy.
The clinical consequence is uncomfortable, because it inverts normal obstetric practice. The period when she most needs someone looking for tuberculosis is the period after we have discharged her.
Why it gets missed, which is not carelessness
Set the symptoms of early tuberculosis beside the symptoms of a normal third trimester.
| Tuberculosis | Also a normal pregnancy |
|---|---|
| Fatigue | Yes |
| Breathlessness | Yes, from splinting and raised oxygen demand |
| Poor appetite | Yes |
| Failure to gain weight | Masked, because she gains weight regardless |
| Night sweats | Common in normal pregnancy |
| Cough | The only one that is not |
Every feature except the cough is expected in a well pregnant woman, and weight loss, the sign that would ordinarily alarm you, is concealed by the fetus and the uterus growing whether or not she is wasting. Pregnancy does not merely fail to reveal tuberculosis. It actively camouflages it.
Which is precisely why the recommendation is not to screen the symptomatic, but to screen everybody. WHO recommends that all pregnant women in high tuberculosis-burden countries and all pregnant women living with HIV are screened at every antenatal visit. In a South African clinic that means a symptom screen every time she comes, not once at booking, and a genuinely low threshold for sending sputum.
Making the diagnosis when you cannot rely on the symptoms
Sputum is still the test that matters. Send it for Xpert, which returns both the organism and rifampicin resistance, and add culture, because a woman starting a six-month regimen deserves a susceptibility result. Pregnancy changes none of this.
What pregnancy does change is the willingness to order a chest radiograph, and the hesitation causes real harm. A chest film with abdominal shielding delivers a fetal dose that is negligible: far below any threshold associated with fetal effects, and vanishingly small beside the consequences of undiagnosed tuberculosis in a mother and her newborn. Radiation is the wrong thing to be frightened of here. Where the clinical suspicion exists, take the film.