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Dynamic changes of Systemic Immune-Inflammation Index during spontaneous term labor and its potential value as a predictive marker of postpartum hemorrhage

This retrospective study demonstrates that the Systemic Immune-Inflammation Index (SII) significantly increases during spontaneous term labor and that elevated SII levels during labor serve as a practical predictive marker for postpartum hemorrhage.

Original authors: wei zeng, Yaluan Bao, Lizhuo Huang, WanYing Zheng, Huafang Lan

Published 2026-07-10

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: wei zeng, Yaluan Bao, Lizhuo Huang, WanYing Zheng, Huafang Lan

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine your body as a bustling city. Usually, when you're pregnant, the city runs a tight "peace treaty" with the new resident (the baby), keeping the immune system calm and quiet so it doesn't attack the tiny guest. But when it's time for the baby to be born, the city has to flip a switch. The peace treaty ends, and a massive, coordinated "construction crew" of immune cells wakes up to help push the baby out.

This study, conducted by researchers at Gutian County Hospital, decided to measure the size of this construction crew using a special score called the Systemic Immune-Inflammation Index (SII). Think of SII as a "chaos meter" for your blood. It's calculated by taking the number of your neutrophils (the first responders), multiplying them by your platelets (the repair crew), and dividing by your lymphocytes (the peacekeepers).

The Big Discovery: Labor is a Loud Party
The researchers looked at 622 women who had healthy, natural births between January 2022 and December 2025. They took blood samples before labor started and again while the women were in labor.

Here is the main finding: The "chaos meter" (SII) went up significantly when labor started.

Before labor: The median SII was 742.60.
During labor: The median SII jumped to 924.30.

The paper explicitly states this increase is real and not just a fluke (P < 0.001). This supports the idea that giving birth isn't just a mechanical event; it's a whole-body inflammatory process. The body is essentially revving its engine to get the job done.

The Warning Sign: When the Engine Overheats
The researchers then asked a crucial question: "Does a super-high 'chaos meter' predict a dangerous problem called Postpartum Hemorrhage (PPH)?" PPH is when a mother loses too much blood after the baby is born.

They split the group into two: those who had normal blood loss (604 women) and those who had PPH (18 women).

Before labor: Both groups had almost identical SII scores. The paper rules out the idea that you can predict PPH just by looking at blood work before the baby arrives.
During labor: The group that ended up with PPH had a much higher SII score (1524.30) compared to the group with normal outcomes (916.15).

The paper suggests that if the "chaos meter" gets too high while you are in labor, it might be a warning sign that the uterus is having trouble contracting properly, leading to bleeding.

How Good is the Prediction?
The researchers used a statistical tool called a "ROC curve" (imagine a radar screen trying to spot a storm) to see how well this SII score could predict PPH.

The radar screen had an accuracy score (AUC) of 0.7099. This isn't a perfect crystal ball, but it's a decent tool.
They found a specific "tipping point" or cutoff: if the SII score during labor is higher than 1619.14, the risk of PPH increases.

What the Paper Does NOT Say
It is important to know what this study doesn't prove.

It does not say that a high SII causes the bleeding. It only suggests a link. The paper admits we still need to figure out the exact "why" and "how."
It does not say this test should be used in every hospital tomorrow. The authors explicitly state that more research is needed to standardize the numbers and confirm these findings in different groups of people.
It does not claim that women with high SII scores will have PPH, only that they are at a higher risk compared to those with lower scores.

The Bottom Line
This study suggests that during a natural birth, your body's inflammation levels naturally rise. However, if those levels get too high during the process, it might be a signal that the uterus is struggling to do its job, potentially leading to bleeding. While the SII score looks like a promising new tool for doctors to keep an eye on, the researchers are careful to say it's a "suggestion" for a new way to manage risk, not a solved mystery or a guaranteed fix just yet.

Technical Summary: Dynamic Changes of Systemic Immune-Inflammation Index during Spontaneous Term Labor and its Potential Value as a Predictive Marker of Postpartum Hemorrhage

Problem Statement
Postpartum hemorrhage (PPH) remains a leading cause of maternal morbidity and mortality globally. While uterine atony is the primary cause, emerging evidence suggests that inflammatory dysregulation plays a critical role in disrupting myometrial contractility. The initiation of natural labor is increasingly understood as a complex physiological inflammatory process involving systemic immune responses. However, there is a lack of accessible, dynamic biomarkers that can track these systemic immune-inflammation changes during spontaneous term labor and correlate them with the risk of PPH. The Systemic Immune-Inflammation Index (SII), calculated from routine complete blood counts, offers a potential composite marker for this purpose, yet its specific trajectory during uncomplicated labor and its predictive utility for PPH require further characterization.

Methodology
This retrospective study was conducted at Gutian County Hospital, analyzing data from January 2022 to December 2025. The cohort consisted of 622 women with uncomplicated, spontaneous full-term pregnancies (37–42 weeks) who delivered vaginally. Participants with pregnancy complications (e.g., gestational diabetes, hypertensive disorders), multiple gestations, or those requiring labor induction or cesarean delivery were excluded.

Data Collection: Peripheral venous blood samples were collected at two distinct time points: prior to the onset of labor and during active labor.
Biomarker Calculation: Complete blood counts were analyzed using a Sysmex xn-2800 hematology analyzer. The SII was calculated for each sample using the formula: $SII = (Neutrophil \times Platelet) / Lymphocyte$ .
Grouping: Participants were categorized into a PPH group (cases, $N=18$ ) and a non-PPH group (controls, $N=604$ ) based on clinical outcomes.
Statistical Analysis: Data normality was assessed via the Kolmogorov–Smirnov test. Non-parametric tests (Mann–Whitney U and Kruskal–Wallis H) were used to compare groups. Outliers were managed according to CLSI guidelines. Receiver Operating Characteristic (ROC) curve analysis was employed to evaluate the predictive performance of SII for PPH.

Key Results

Dynamic Changes in Uncomplicated Labor: In the overall cohort of 622 women, the SII level during spontaneous labor was significantly higher than the pre-labor baseline ( $P < 0.001$ ). The median SII increased from 742.60 (IQR: 592.44–974.19) pre-labor to 924.30 (IQR: 654.28–1303.53) during labor.
Comparison Between PPH and Non-PPH Groups:
- Pre-labor: No significant difference in SII levels was observed between the PPH and non-PPH groups ( $P > 0.05$ ).
- During Labor: The SII level was markedly higher in the PPH group compared to the non-PPH group ( $P < 0.05$ ). Specifically, the median SII for the PPH group was 1524.30 (IQR: 815.66–2488.58), compared to 916.15 (IQR: 650.22–1286.3) for the control group.
Predictive Value: ROC analysis indicated that SII measured during labor has moderate predictive value for PPH, yielding an Area Under the Curve (AUC) of 0.7099 (95% CI: 0.5812–0.8386). The optimal cutoff value was determined to be 1619.14, corresponding to a maximum Youden index of 0.358.

Significance and Claims
The authors posit that the significant rise in SII during natural labor in otherwise uncomplicated pregnancies provides experimental support for the theory of "systemic immune inflammation" as a driver of labor onset. This finding aligns with the understanding that labor involves a coordinated activation of local and systemic inflammatory pathways.

Regarding clinical utility, the study claims that an elevated SII during labor may serve as a practical, cost-effective predictive marker for postpartum hemorrhage. Because SII is derived from routine complete blood counts, it offers a feasible framework for dynamic monitoring in clinical settings. The authors suggest that high SII levels could help identify women at increased risk for PPH, potentially aiding in risk stratification and management strategies.

Limitations and Future Directions
The paper maintains a modest tone regarding its conclusions. It acknowledges that the findings are based on a retrospective, single-center study with a relatively small number of PPH cases (18). The authors emphasize that while the association is promising, the study does not establish a definitive causal mechanism linking SII components directly to myometrial contractility failure. They note that future work requires standardized cutoffs, prospective validation in diverse cohorts, and further investigation into the temporal-spatial regulatory mechanisms between inflammation and myometrial function before SII can be routinely adopted for clinical risk stratification.

Technical Summary: Dynamic Changes of Systemic Immune-Inflammation Index during Spontaneous Term Labor and its Potential Value as a Predictive Marker of Postpartum Hemorrhage

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