Maternal sepsis is a life-threatening condition in which infection triggers organ dysfunction during pregnancy, childbirth, after abortion, or the postpartum period. It remains a major cause of preventable maternal illness and death worldwide.
Global estimates suggest that maternal sepsis and related infections accounted for approximately 19 million cases in 2021, although the true burden is likely higher because definitions, surveillance, and reporting vary substantially between health systems.
Pregnancy itself is not an immunodeficient state. Instead, the maternal immune system is continuously recalibrated to support the fetus while preserving protection against infection. Sepsis is also an immunologically dynamic condition—but its changes are maladaptive, producing some combination of excessive inflammation, immune suppression, vascular injury, and organ dysfunction.
Understanding where these two processes overlap—and where they differ—could improve the recognition and treatment of maternal sepsis.
Why sepsis can be difficult to recognize
Normal pregnancy changes cardiovascular, respiratory, renal, and hematologic physiology in ways that can resemble early sepsis.
Blood pressure and systemic vascular resistance normally fall, while blood volume, heart rate, and cardiac output rise. White-cell counts increase, especially neutrophils, and mild thrombocytopenia is common. During labor and shortly after delivery, inflammation increases further.
These normal changes can overlap with sepsis-related abnormalities. C-reactive protein and, in some circumstances, procalcitonin may rise around labor, reducing their specificity. A high white-cell count may reflect pregnancy or infection, while a low count can be a concerning sign in a patient with severe infection.
The postpartum period presents an additional challenge: tissue injury and physiologic inflammation from labor can resemble infection, yet serious infections may progress rapidly.
Pregnancy also alters the body’s physiological reserve. Pregnant patients have increased susceptibility to severe outcomes from some infections, including influenza, malaria, listeriosis, urinary tract infections, and invasive group A streptococcal disease.
For clinicians, the implication is important: sepsis assessment in pregnancy cannot rely on a single laboratory value or on nonpregnant reference ranges alone. Symptoms, trends, organ function, suspected infection, gestational age, and postpartum status all need to be considered together.
The pregnancy “immune clock”
Maternal immunity changes across gestation rather than remaining static.
Early pregnancy
The first trimester requires carefully regulated local inflammation at the maternal–placental interface. Decidual natural killer cells, macrophages, neutrophils, and other cells help support implantation, placental development, and remodeling of the uterine blood supply.
At the same time, systemic immune tolerance begins to increase. Regulatory T cells and tolerogenic immune programs help prevent rejection of the fetus.
Mid-pregnancy
The second trimester is generally characterized by a more anti-inflammatory and tolerant environment that supports fetal and placental growth. Regulatory T cells remain important, while some inflammatory T-cell responses are restrained.
This is not equivalent to generalized immune weakness. Immune surveillance continues, but the balance between defense and tolerance is adjusted.
Late pregnancy
During the third trimester and labor, inflammatory activity increases again. Neutrophils, macrophages, T cells, prostaglandins, and matrix-remodeling enzymes contribute to cervical ripening, membrane rupture, uterine contraction, and delivery.
This predictable sequence is sometimes described as the “immune clock” of pregnancy. The difficulty is that sepsis can occur against any point on this changing baseline.
How sepsis differs
Sepsis involves a dysregulated response to infection rather than a normal, coordinated immune transition.
Early sepsis may produce excessive activation of inflammatory pathways, including TNF-α, IL-1β, IL-6, NF-κB, and inflammasome signaling. This can increase vascular permeability, cause capillary leak, impair perfusion, and contribute to shock and organ dysfunction.
At the same time, anti-inflammatory mechanisms are activated. If they become excessive or prolonged, patients may develop immune paralysis, lymphocyte apoptosis, T-cell exhaustion, reduced antigen presentation, and impaired antibody responses.
These processes can occur simultaneously rather than in two neatly separated phases. A patient may have severe inflammation in one compartment and immune suppression in another.
Blood counts can provide clues but are not definitive. Pregnancy-related neutrophilia and postpartum leukocytosis may obscure an abnormal response. In sepsis, neutrophilia may be followed by neutropenia, while profound lymphopenia and thrombocytopenia can indicate severe immune and systemic dysfunction.
Numerical recovery also does not necessarily mean immunologic recovery. After sepsis, lymphocyte counts may normalize before T-cell function has fully returned, and some survivors experience prolonged susceptibility to secondary infections.
Where pregnancy and sepsis overlap
Pregnancy and sepsis share changes in several immune compartments:
Neutrophil activity and trafficking.
Monocyte and macrophage polarization.
T-cell differentiation and function.
Cytokine and chemokine signaling.
Complement and coagulation activation.
Cellular metabolism and mitochondrial function.
The difference lies in regulation, timing, and magnitude. Pregnancy uses these pathways in a controlled, phase-specific manner. Sepsis can activate them excessively, persistently, or inappropriately.
This overlap may help explain why infection can be difficult to identify during pregnancy and why organ dysfunction may develop rapidly once compensatory mechanisms fail.
The placenta adds another layer. Maternal infection can alter placental inflammatory and vascular signaling and may contribute to fetal inflammatory responses, preterm birth, fetal growth restriction, stillbirth, and adverse neonatal outcomes. These outcomes do not occur in every maternal infection, but they underscore the importance of early recognition and coordinated maternal–fetal care.
Toward precision medicine
The maternal immune response is influenced by gestational age, hormones, genetic background, metabolic health, ethnicity, the fetus, the pathogen, the microbiome, and the clinical environment.
These factors may help explain why patients with apparently similar infections follow different clinical trajectories. Future precision approaches could include:
Cytokine and immune profiling to distinguish hyperinflammation from immune exhaustion.
Transcriptomic and genomic testing to identify disease endotypes and predict deterioration.
Metabolic and mitochondrial profiling to detect bioenergetic failure.
Artificial intelligence to integrate clinical trends, laboratory results, and biological data.
These strategies remain investigational. Signatures developed in nonpregnant patients cannot simply be transferred to pregnancy because normal immune and hormonal states change across trimesters.
Potential treatments targeting cytokines, inflammasomes, neutrophil extracellular traps, epigenetic pathways, or metabolism also require pregnancy-specific evaluation. Placental transfer, fetal development, pharmacokinetics, and long-term child outcomes must be considered.
Precision medicine should complement—not delay—urgent antimicrobial therapy, source control, hemodynamic support, respiratory care, and obstetric management.
What pregnancy may teach sepsis research
Pregnancy provides a natural example of immune recalibration. The maternal system must tolerate the fetus, defend against pathogens, adapt blood flow, and move between inflammatory states without losing control.
Studying these mechanisms may help researchers design phase-specific therapies for sepsis beyond pregnancy. The goal would not be to reproduce pregnancy’s immune state, but to understand how timing, tissue context, hormones, and metabolic feedback influence inflammatory disease.
Source: eBioMedicine
