Early Postpartum IL-10 and IL-37 Concentrations in Women with Gestational Diabetes Mellitus

Introduction

Gestational diabetes mellitus (GDM) affects approximately 5% to 22% of pregnant women, depending on diagnostic criteria and population characteristics [1–3]. GDM is associated with a proinflammatory state and a range of maternal and fetal complications. In normal pregnancy, insulin resistance increases during the second half of gestation due to placental hormonal changes and maternal weight gain. In most women, normoglycemia is maintained via compensatory insulin secretion by the pancreatic islets of Langerhans [4–6].

In GDM, this compensation is insufficient. The pathophysiology shares characteristics with type 2 diabetes mellitus (T2DM), including chronic low-grade inflammation and elevated levels of proinflammatory cytokines that impair insulin signaling, leading to further insulin resistance and β-cell stress. After delivery – and the removal of the placenta as a key source of diabetogenic hormones – women with GDM and their children display persistently increased risks of developing T2DM, obesity, cardiovascular disease, and metabolic syndrome [1,7–9].

Recent studies have focused on the role of anti-inflammatory cytokines in regulating immune tolerance during pregnancy. Interleukin (IL)-10 is a pleiotropic cytokine secreted by various immune cells, including natural killer cells, macrophages, T and B lymphocytes, and dendritic cells. It regulates cellular metabolism and plays a critical role in suppressing proinflammatory responses [10–12]. In women with GDM, IL-10 levels may be altered, although published findings remain inconsistent. For example, Lucia et al reported increased IL-10 concentrations in the amniotic fluid of women with GDM relative to controls [13].

IL-37, a member of the IL-1 family, has emerged as a potent anti-inflammatory cytokine that suppresses both innate and adaptive immune responses, primarily through inhibition of dendritic cell maturation [14–18]. IL-37 is expressed in immune and epithelial cells, as well as lymphoid and reproductive tissues [19–22]. Recent research has linked reduced IL-37 levels to increased placental inflammation and impaired metabolic regulation in pregnancies complicated by GDM [18].

Despite growing evidence that these cytokines are involved in the pathophysiology of GDM, data remain limited regarding their early postpartum concentrations and potential associations with clinical parameters. Therefore, this study aimed to compare serum concentrations of IL-10 and IL-37 during the early postpartum period between women with GDM and healthy controls. We also examined relationships between IL levels and selected maternal factors, including gestational weight gain, physical activity, hydration status, anthropometric characteristics, substance use, and family history of metabolic disease – variables previously associated with immune and metabolic regulation in pregnancy [23,24].

Given the inflammatory background of GDM and the potential of ILs to serve as biomarkers of metabolic dysfunction, this study was designed to compare postpartum IL-10 and IL-37 levels between women with and without GDM. We hypothesized that altered interleukin profiles reflect persistent meta-inflammation after delivery and could serve as early indicators of long-term metabolic risk in affected mothers.

Material and Methods

STUDY DESIGN AND PARTICIPANTS:

This cross-sectional study included 80 women of European ethnicity who gave birth at the Department of Obstetrics and Perinatology, Medical University of Lublin, Poland, between November 2022 and January 2024. All data were collected during the early postpartum period, within 24–72 h after delivery.

WERE DIVIDED INTO 2 GROUPS:

Inclusion criteria were:

All participants had a fasting plasma glucose level below 92 mg/dL before 10 weeks of gestation. Written informed consent was obtained from all participants. The study was approved by the Bioethics Committee of the Medical University of Lublin (approval no. KE-0254/61/2020; 26 March 2020).

DATA COLLECTION AND CLINICAL ASSESSMENTS:

Data were collected using a standardized protocol and included the following:

LABORATORY TESTING:

Peripheral venous blood samples were collected from all participants on the morning of the first postpartum day. After centrifugation, serum samples were aliquoted and stored at -80°C until analysis.

Assays were performed in duplicate, in accordance with the manufacturer’s instructions. Intra-assay and interassay coefficients of variation were below 10% and 12%, respectively. The sensitivities of the assays were 2 pg/mL for IL-10 and 5 pg/mL for IL-37.

STATISTICAL ANALYSIS:

All data were entered into Microsoft Excel (Microsoft Corp., USA) and analyzed using MedCalc v15.8 (MedCalc Software Ltd., Belgium) and Statistica v13 (TIBCO Software Inc., USA). Categorical variables were expressed as absolute numbers and percentages. Continuous variables were assayed for normality using the D’Agostino-Pearson test. Non-normally distributed variables were summarized as medians with interquartile ranges (IQRs) and compared using the Mann-Whitney U test or Kruskal-Wallis analysis of variance, as appropriate. Correlations between continuous variables were assessed using Spearman’s rank correlation coefficient. P-values <0.05 were considered statistically significant.

Variables included in the correlation analyses were selected based on known or potential associations with immune and metabolic regulation during pregnancy and the early postpartum period. These included anthropometric measures (e.g., pre-pregnancy BMI, waist circumference), hydration status (e.g., ECW, extracellular-to-intracellular water [E/I] ratio) [25–27], behavioral factors (e.g., physical activity, smoking, alcohol use) [28,29], and selected neonatal outcomes (e.g., cord blood pH) [30]. Their inclusion was intended to detect possible relationships with postpartum cytokine concentrations based on biological plausibility and evidence from the literature.

Results

GROUP CHARACTERISTICS:

Statistically significant differences between the GDM and control groups were observed regarding place of residence, parity, mode of delivery, and gestational weight gain (Tables 1, 2). Women with GDM were more likely to be primigravid and more frequently undergo cesarean section compared with healthy controls (P<0.05).

In the GDM group, significantly higher percentages of participants were in their first pregnancy (56.7% vs 30%; P=0.0174) and experiencing their first delivery (60% vs 30%; P=0.0218) at the time of the study. Additionally, cesarean section was performed more frequently in the GDM group than in the control group (46.7% vs 12%; P=0.0021).

A detailed analysis of gestational weight gain revealed significant differences between the groups. In the GDM group, a higher percentage of women gained 20–25 kg during pregnancy (16.7%), whereas no such cases were observed in the control group (P=0.0028). These findings suggest a tendency toward excessive weight gain among women with GDM, which may contribute to persistent postpartum metabolic alterations. Detailed data regarding diet, physical activity, addictions, nutritional status, and family history of diabetes and obesity are presented in Table 3.

LIFESTYLE AND FAMILY HISTORY:

Significant differences were observed in the prevalence of a family history of obesity and diabetes, both of which were more common in the GDM group (P<0.05). Regarding smoking status, participants in the GDM group reported more frequent daily exposure to tobacco smoke (P=0.007). In terms of physical activity, women with GDM were less likely to participate in regular moderate-intensity exercise, with statistically significant differences identified across activity frequency categories (P=0.0133). These comparisons indicate distinct behavioral profiles between the groups but do not imply causation or predictive value.

BODY COMPOSITION AND HYDRATION:

Women in the GDM group had significantly greater skinfold thickness, TBW, and ICW values compared with controls (P<0.05), as shown in Table 4. These differences may reflect persistent postpartum metabolic alterations.

Skinfold thickness measurements were significantly higher in the GDM group than in the control group (21.5 mm vs 19 mm; P=0.0106). Additionally, significantly greater TBW (34.6 L vs 31.9 L; P=0.0317) and ICW (18.5 L vs 16.5 L; P=0.0326) values were observed in the GDM group.

Detailed descriptive characteristics and intergroup comparisons of selected cytokine concentrations are presented in Table 5.

No statistically significant difference in serum IL-10 levels was observed between the groups. However, IL-37 concentrations were significantly lower in the GDM group (median: 0.1 pg/mL [0.01–17]) than in the control group (median: 90.1 pg/mL [25.7–258.2]; P<0.0001). Despite the wide range of values, these findings are consistent with previous reports of reduced IL-37 levels in GDM, although interstudy variability may result from differences in ELISA sensitivity or sample handling protocols [31].

Table 6 presents detailed correlations between the assessed cytokines and selected clinical variables in the GDM group.

In the GDM group, serum IL-10 levels demonstrated significant negative correlations with several anthropometric and hydration-related variables, including:

A representative correlation is depicted in Figure 1.

In contrast, IL-37 levels in the GDM group were positively correlated with gestational age at delivery (rho=0.367; P=0.0462) and negatively correlated with reported daily water intake (rho=−0.364; P=0.0483). These findings may indicate an interaction between hydration status and cytokine regulation in the early postpartum period.

Detailed correlations between cytokines and selected clinical variables in the control group are presented in Table 7.

In the control group, IL-10 showed significant positive correlations with overhydration (rho=0.382; P=0.0062) and E/I ratio (rho=0.402; P=0.0038). Furthermore, IL-10 showed significant negative correlations with physical activity before pregnancy (rho=−0.279; P=0.0495), physical activity during pregnancy (rho=−0.344; P=0.0143), skinfold thickness (rho=−0.336; P=0.0171), body cell mass (rho=−0.282; P=0.0473), and Apgar scores (rho=−0.288; P=0.0424). The positive correlation between IL-10 and the E/I ratio in the control group is illustrated in Figure 2.

Except for the negative correlation between IL-37 and alcohol consumption 3 months before pregnancy (rho=−0.299; P=0.0350), no other statistically significant correlations were observed in the control group.

Discussion

GDM remains a major challenge in modern medicine due to its adverse effects on mothers and their children. In mothers, a diagnosis of GDM substantially increases the risk of subsequent T2DM onset. Children born to mothers with GDM also have higher risks of obesity and diabetes in the future. As global obesity rates continue to rise, efforts to identify effective strategies to prevent and manage obesity – and its associated metabolic consequences – have become a public health priority.

The development of novel diagnostic and therapeutic targets for GDM remains an important medical objective. Our study, conducted in obstetric units during the early postpartum period (prior to hospital discharge), focused on a critical window for maternal physiological and metabolic adaptation. Research during this phase may guide the development of postpartum care recommendations aimed at preventing future lifestyle-related diseases.

This study contributes to the existing literature through its evaluation of IL-10 and IL-37 concentrations during the immediate postpartum period – a phase characterized by immunologic transition after placental removal. Assessment during this period may reveal residual meta-inflammation in women with GDM and aid early risk stratification for long-term metabolic complications.

In our cohort, a substantial percentage of women with GDM resided in urban areas. Nearly 77% of these women lived in cities and towns with populations between 50 000 and 500 000, whereas 54% of healthy controls resided in rural areas or towns with fewer than 50 000 inhabitants. Similar findings were reported by Xu et al [23], who demonstrated that women residing in urban environments were more likely to develop GDM relative to women in rural areas.

Variables were selected for inclusion in correlation analyses with IL-10 and IL-37 levels based on their relevance to metabolic and inflammatory statuses during pregnancy. Measures such as pre-pregnancy BMI and hydration parameters reflect maternal metabolic load [25,26], whereas behavioral and lifestyle factors may influence systemic inflammation and immune responses [28,29]. Although some identified associations were exploratory and not previously described, they may indicate early postpartum immunometabolic interactions that warrant further investigation.

In the present study, women with GDM were more likely to have been exposed to passive smoking in the preceding year relative to healthy mothers; they also were more likely to report lower physical activity during pregnancy. Na et al examined the influence of passive smoking on GDM occurrence in a cohort of more than 3000 women [24]. After adjustments for age, BMI, ethnicity, education, occupation, and parity, the authors found that passive smoking was associated with a 1.4-fold increased risk of GDM onset; an even stronger association was observed among nulliparous women.

The role of physical activity in GDM prevention has been emphasized within multiple professional society recommendations. Sitzberger et al evaluated 99 women with GDM and 107 healthy pregnant women [32]. They reported that the frequency of physical activity was significantly higher in the control group, whereas objective physical fitness was lower among women with GDM. Notably, women who were physically inactive before pregnancy had a 3-fold higher risk of GDM onset compared with those who maintained regular physical activity.

Compared with healthy pregnant women, we found that weight gain during pregnancy was greater among women with GDM who exhibited overweight or obesity before conception. This observation aligns with findings from 2 independent research groups, Ćwiek et al [33] and Tranidou et al [34]. Additionally, a family history of diabetes or obesity increases the likelihood of GDM onset, as demonstrated in studies involving 912 pregnant women [35], 317 mothers [36], and 1117 women [37]. We also observed that pregnant women with GDM were more likely to deliver via cesarean section than their healthy counterparts, consistent with findings by Gascho et al [38] and Eshetu et al [39].

In the present study, postpartum women with GDM exhibited significantly lower IL-37 concentrations relative to controls, suggesting that IL-37 is protective against GDM onset during pregnancy. Notably, most women in the GDM group received insulin therapy during pregnancy. Exogenous insulin has been shown to influence placental signaling pathways, including the phosphoinositide-3-kinase (PI3K)/protein kinase B (AKT) and mitogen-activated protein kinase pathways, which regulate cytokine production, oxidative stress, and inflammatory responses [40–42]. Recent studies have indicated that insulin may alter IL-10 and IL-37 expression patterns by modulating trophoblast and maternal immune cell activities. These effects may partly explain the altered cytokine profiles observed in the present study; they highlight the importance of considering treatment modality when interpreting immunologic findings in GDM populations [43].

Similar findings were reported by Yu et al [31], who observed reduced IL-37 concentrations in the serum (33% lower), placental chorionic villi (49% lower), umbilical arteries (48% lower), and umbilical veins (57% lower) of women with GDM relative to those parameters among women without GDM. Wang et al also reported decreased IL-37 expression in GDM and demonstrated a negative association between miR-657 and IL-37, suggesting that miR-657 specifically regulates IL-37 and may promote mononuclear macrophage proliferation. Furthermore, miR-657 enhanced the production of inflammatory cytokines (IL-6 and tumor necrosis factor-α) and activated nuclear factor-κB (NF-κB) in lipopolysaccharide-induced mononuclear macrophages; these effects were significantly inhibited by treatment with exogenous recombinant IL-37 [44].

A review by Wang emphasized the role of reduced IL-37 expression in GDM onset, leading to diminished anti-inflammatory protection in both local (placental) and systemic responses, and resulting in enhanced placental inflammation among women with GDM [45]. Although our study also demonstrated reduced postpartum IL-37 levels in women with GDM, the precise role of this cytokine in GDM pathogenesis remains unclear. Given the cross-sectional and postpartum design of the present study, causality and temporal relationships could not be established. Future research should examine whether persistently low IL-37 levels after delivery are associated with increased risks of T2DM onset or impaired glycemic control in this population.

No statistically significant differences in IL-10 levels were detected between the GDM and control groups in the present study, suggesting that IL-10 is not associated with GDM. Similar conclusions were drawn by Cai et al, who reported that serum IL-10 concentrations were not significantly associated with an increased risk of GDM onset [46]. Our correlation analyses were exploratory and intended to identify potential relationships of cytokine levels with anthropometric or hydration-related variables. Although some associations lacked strong biological plausibility or may have been influenced by sampling timing, the observed patterns lead to hypotheses that merit further investigation in prospective studies with larger cohorts and mechanistic endpoints. Comparable results have been reported by Vrachnis et al [47], Moreli et al [48], and van Exel et al [49], who found no significant differences in IL-10 concentrations between women with and without GDM.

Among the observed correlations of ILs with various parameters, a particularly noteworthy and difficult-to-interpret finding was the relationship between IL-10 and the E/I ratio. IL-10 concentrations showed a positive correlation with the E/I ratio in healthy women; they showed a negative correlation with this parameter among women with GDM. This result is unexpected, given that neither IL-10 levels nor the E/I ratio significantly differed between groups. One possible explanation may involve altered fluid distribution due to low-grade inflammation in GDM, which could modulate cytokine signaling and osmotic regulation mechanisms [50].

IL-10, an anti-inflammatory cytokine, can exceed normal levels in disease states or during dysregulation of the immune response. IL-10 concentrations may be affected by various environmental and physiological factors, including hydration status, which has been implicated in immune modulation. Previous studies have demonstrated that oral water intake and exposure to thermal mineral waters can influence IL-10 levels [51,52], suggesting a complex interaction between hydration and anti-inflammatory cytokine activity. Further research is needed to clarify these mechanisms in postpartum women with GDM. The importance of adequate water intake – particularly among breastfeeding women – and the broader connections between hydration and immune function are well established. Multiple studies have examined the relationships of the anti-inflammatory cytokine IL-10 with oral water consumption and exposure to sulfurous thermal waters [51,53].

Conclusions

This study demonstrated that postpartum women with a history of GDM exhibited significantly lower IL-37 concentrations relative to healthy controls in the early days after delivery. This finding may indicate persistent impairment of anti-inflammatory mechanisms and immune regulation extending beyond pregnancy. In contrast, IL-10 levels did not significantly differ between groups; however, correlation analyses revealed distinct patterns in relation to metabolic and hydration parameters, suggesting a more complex and possibly indirect role for this cytokine in postpartum immunometabolic interactions. The observed alterations in IL levels may have been influenced by factors such as insulin therapy during pregnancy, which is known to modulate placental signaling and cytokine expression. These findings highlight the potential relevance of IL-37 as a biomarker of persistent meta-inflammation in women with a history of GDM and may help identify individuals with higher risks of subsequent T2DM or other cardiometabolic conditions.

Although correlation analyses revealed several statistically significant relationships, not all demonstrated clearly defined causal mechanisms. The selection of clinical and behavioral variables for evaluation was guided by biological plausibility and supported by evidence linking adiposity, hydration status, and lifestyle behaviors with immune regulation during pregnancy and the postpartum period [25–29]. These findings should be regarded as exploratory and hypothesis-generating, reflecting the complexity of postpartum immunometabolic interactions in women with GDM.

Incorporating cytokine profiling into postpartum monitoring – particularly among insulin-treated patients with GDM – may provide a valuable approach for the early detection of inflammatory dysregulation. Such detection could facilitate the development of personalized recommendations for diet, physical activity, and long-term follow-up strategies for mothers and their children, ultimately aiming to reduce the burden of chronic lifestyle-related diseases.