Maternal serum level of TNF-α in Nigerian women with gestational diabetes mellitus

Introduction alterations in the circulating level of tumour necrosis factor-α (TNF-α) has been proposed to be involved in the pathogenesis of gestational diabetes mellitus (GDM), but its role is not completely understood, findings from studies done across different ethnic groups are often inconsistent. We carried out this study to determine maternal serum level of TNF-a and it's association with body weight status in a group of Nigerian women with GDM. Methods a cross sectional analytical study conducted among 169 pregnant women, 85 with GDM and 84 with normal gestation. Diagnosis of GDM was made between 24-28 weeks gestation according to the WHO diagnostic criteria. Maternal serum level of TNF-α was measured and compared between the study groups. Results maternal serum TNF-α level was significantly higher in the pregnant women with GDM than in the controls (2.50 ± 0.30 vs. 2.10 ± 0.30 pg/ml, p < 0.05). Also when comparing the serum TNF-α levels of the pregnant women with GDM and the controls for each level of body mass index, serum TNF-α levels remained significantly higher in both the normal weight and overweight pregnant women with GDM compared to their matched controls (2.40 ± 0.30 vs. 1.90 ± 0.20 pg/ml, p < 0.05) and (2.60 ± 0.30 vs. 2.30 ± 0.20 pg/ml, p < 0.05) respectively. Conclusion it is concluded that pregnant women with GDM in this study have higher maternal serum TNF-α level compared to the pregnant women with normal glucose tolerance regardless of body weight status.


Introduction
Gestational diabetes mellitus (GDM) is defined as any degree of glucose intolerance with onset or first recognition during pregnancy [1]. The prevalence of gestational diabetes mellitus has been increasing dramatically worldwide over the last two decades [2]. In Nigeria the prevalence ranges from 3.4-13.9% across the different regions of the country [3][4][5][6][7]. Gestational diabetes mellitus is associated with increased obstetric and perinatal morbidity and mortality [2]. Despite remarkable progress made in the field of endocrinology, the exact mechanism implicated in the pathogenesis of gestational diabetes mellitus is still not completely understood.
Recently the role of inflammatory cytokines especially TNF-α has been increasingly investigated but findings are inconsistent especially across different ethnic groups [8][9][10][11][12][13][14][15][16][17]. While ethnicity is one of the factors that influence production of cytokines during pregnancy [18], studies on the association between alterations in the maternal circulating level of TNF-α and development of gestational diabetes mellitus among black African women are limited. We are not aware of any study done in Nigeria among women with gestational diabetes mellitus. This study was therefore designed to compare maternal circulating TNF-α levels between Nigerian pregnant women with and without gestational diabetes mellitus. age, parity and gestational age were all obtained from the subjects at the time of enrolment. Gestational age was based on the report of ultrasound scan. Body mass index (BMI) was calculated as the ratio of weight in kilogram to square of height in meters and expressed as kg/m2. The two-hour 75g oral glucose tolerance test was performed in the morning (8:00am-10:30am) following 10-12 hours overnight fast. A fasting blood sample was drawn for measurement of fasting serum glucose and TNF-α. Two-hour blood sample after an oral glucose load was taken for measurement of 2-hour serum glucose.

Results
Demographic characteristics of the study subjects are presented in Table 1. Both the study groups were of similar maternal age,  Table 2. Serum level of TNF-α was significantly higher among the pregnant women with gestational diabetes mellitus compared to the controls (2.50 ± 0.30 vs. 2.10 ± 0.30 pg/ml, p < 0.05). When the maternal serum TNF-α levels of the pregnant women with gestational diabetes mellitus and the controls were compared for each level of BMI (Table 3), serum TNF-α levels remained significantly higher in both the normal weight and overweight pregnant women with gestational diabetes mellitus compared to their matched controls (2.4 ± 0.3 vs. 1.9 ± 0.2 pg/ml, p < 0.05) and (2.6 ± 0.3 vs. 2.3 ± 0.2 pg/ml, p < 0.05) respectively (Figure 1).

Discussion
This study has shown that the pregnant women with gestational diabetes mellitus have higher serum TNF-α levels than the pregnant women with normal gestation. This finding of increased serum TNFα level in pregnant women with gestational diabetes mellitus has been reported in many previous studies [8,[11][12][13]. Also in line with the results of this study Laetitia et al. reported that higher maternal serum level of TNF-α is a significant predictor of developing gestational diabetes mellitus [3]. When comparing maternal serum TNF-α levels of the study subjects for each level of body mass index, serum TNF-α levels remained significantly higher in both the normal weight and overweight pregnant women with gestational diabetes mellitus compared to their matched controls. The same finding was reported by McLachlan et al. [9], although in a study with a relatively smaller sample size (19 GDM and 19 controls). However, the findings of Saucedo et al. did not show significant difference between serum TNF-α levels in pregnant women with gestational diabetes mellitus compared to normal controls. Their negative findings might be due to the differences in timing of maternal blood collection, assay methods used and ethnicity of the study subjects [10]. The discrepancy might also be due to the greater BMI of their study subjects (mean BMI of 30kg/m2 and 28kg/m2 for the GDM and control groups respectively).
The finding of increased maternal inflammatory cytokine (TNF-α) among women with GDM as compared to those with normal gestation, in this study, further supports the previous reports that suggests GDM is associated with amplified inflammatory response.

Conclusion
We conclude that among the pregnant women in this study, those with gestational diabetes mellitus have higher serum TNF-α levels than the pregnant women with normal glucose tolerance regardless of body weight status, suggesting that alterations in the circulating level of TNF-α might be related to the pathogenesis of gestational diabetes mellitus. We recommend larger prospective studies within the population that would examine the mechanism of alteration of the maternal circulating TNF-α level and its pattern from first through third trimester in pregnant women with gestational diabetes mellitus.
What is known about this topic  Gestational diabetes mellitus results from an imbalance between insulin resistance and insulin secretion capacity during pregnancy;  Pro-inflammatory cytokines might cause insulin resistance by inhibiting insulin signal transduction.

Acknowledgments
We would like to thank the heads, departments of Chemical Pathology and Obstetrics and Gynaecology, Ahmadu Bello University, Zaria, Nigeria for their support. We are also grateful to all the study participants. There was no external funding source. Table 1: clinical characteristics of the study participants Table 2: biochemical profiles of the study participants Table 3: biochemical profiles of the study participants in relation to body mass index