Pregnant women suddenly or for the first time during pregnancy develop glucose intolerance, which is called gestational diabetes [1]. Insulin-dependent diabetes and gestational diabetes both cause problems for the neonates including congenital defects; increased obstetric complications; increased birth trauma in the neonate; and heart, respiratory, renal and  cerebral complications; metabolic disorders (hypoglycemia, hypocalcemia, hyperbilirubinemia); coagulation disorders; and polycythemia. These factors have a significant effect on neonate mortality and morbidity [2,3]. Therefore, recognizing the effective factors in diabetes and controlling them, can prevent or reduce the incidence of complications in the neonate. A wide range of vitamins, minerals and nutrients are effective in regulating blood glucose and adding some of these micronutrients to the diet of diabetics can reduce the damage caused by the disease. Chromium supplementation in humans has improved glucose tolerance and leads to lower fasting blood sugar, increased insulin function [4]. Zinc has also been a key factor in production of insulin by beta cells and has protective effects against the destruction of these cells. Its deficiency is a predisposing factor for diabetes and is associated with undesirable effects on the fetus [5,6]. Selenium is another micronutrient that as an essential element plays an important role in the function of antioxidants such as glutathione peroxidase [7]. On the other hand, due to the structure of insulin like, its anti-diabetic function has been proposed [8]. In recent years, human and animal evidence has shown a significant relation between copper levels and abnormal glucose metabolism [9]. According to the importance of these micronutrients, we decided to study the levels of selenium, chromium, zinc and copper in pregnant women with gestational diabetes compared to healthy pregnant women.  

The present case-control study was performed on 100 pregnant mothers referred to Imam Reza Hospital in Mashhad, Iran. After the approval of the project in the ethics committee of Mashhad University of Medical Sciences with the code of ethics fifty healthy pregnant women were considered as control group and the case group included 50 pregnant mothers who were defined as gestational diabetes by definition. For women with gestational aged 24-28 weeks, glucose tolerance test was performed after 8-14 hours of fasting and according to the gestational diabetes was diagnosed after drinking a solution containing 75 grams of glucose. Normal results in level of fasting blood glucose <5.1 mmol / L (92 mg / dL) at baseline, <10.0 mmol / L (180 mg / dL) at 1 h, <8.5 mmol / L (153 mg / dL) at 2 h. Was defined and if one or more of the tests in pregnant women were abnormal, it was specified as gestational diabetes [10].Conscious consent was obtained from them to participate in the study. Maternal demographic information including age, weight, height as well as parity, positive family history of diabetes in first-degree relatives, employment and history of other diseases and consumption of formula during infancy were recorded in the checklist. To prepare a sample from both case and control groups, 6 cc of blood was taken from peripheral arteries and poured into a dry tube. Its serum was separated and frozen and at the end of collecting the samples, all of them were measured in terms of micronutrients including zinc, copper, selenium and chromium. Sampling was done at the time of maternal visit and before delivery room. In this way, every mother with gestational diabetes who referred to the hospital for delivery, after obtaining the consent to participate in the project, a blood sample was taken from her just before delivery to check for micronutrients and at the same time, a sample was taken from a healthy pregnant mother who referred for delivery as a control group before labor. After data collection, they were processed with spss16 software and with t-test, Mann-Whitney and frequency distribution were analyzed. P value less than 0.05 was considered significant.

The mean age of diabetic and non-diabetic pregnant mothers was 32.33 ± 5.92 and 26.32 ± 5.38 years respectively which is higher in diabetic mothers (p <0.01). Indeed their mean weight was 82.87 ± 10.81 and 73.18 ± 10.6 kg, respectively, which was significantly higher in diabetic mothers than non-diabetics (p <0.01) but this difference was not significant in maternal height (Table 1).

Table 1: Comparison of mothers' characteristics in case and control groups.

There  was a significant difference between the case and control groups in terms of family history of diabetes in first-degree relatives ,history of formula fed mothers during infancy , gravid > 3  and low gestational so that were more common in women with gestational diabetes (p < 0.05).

Serum levels of zinc, copper, selenium and chromium between the two groups of gestational diabetic and non-diabetic pregnant mothers were compared, but there was no significant difference between two groups (p> 0.05) (Table 2).

Table 2: Comparison of micronutrient levels in case and control groups.

Gestational diabetes is a multifactorial disease including genetic and environmental factors which affect insulin sensitivity [11]. Several studies have reported obesity and maternal weight gain are higher risk of gestational diabetes and preeclampsia [12]. The results of present study also showed that the pregnant women with gestational diabetes had more weight than the control group. In addition, we indicated in our study that the mean age of mothers in the group with gestational diabetes was significantly higher than the control group. This finding was consistent with previous studies and maternal age over 30 years was reported as a risk factor for gestational diabetes [13,14]. In other words, the same as other studies maternal weight gain and age increase the risk of gestational diabetes. Our research showed that factors such as gravid more than 3, formula fed mothers during infancy, family history of diabetes and preterm birth in gestational diabetes group were significantly more than non-diabetic mothers. In a meta-analysis published in 2017, a positive family history of diabetes was identified as one of the most important risk factors for gestational diabetes [15].

Abu-Heija showed that with increasing parity, the incidence of gestational diabetes will increase, so that the incidence of gestational diabetes increased from 3.5% in nulliparous women to 14.6% in women with parity greater than 4 and these results are consistent with ours [3]. In our study also parity greater than 3 was significantly associated with gestational diabetes. In results of Patelarou in a systematic review has been observed that short periods of breastfeeding or lack of breastfeeding will be a risk factor for type 1 diabetes in later life [16], but we also found this association with gestational diabetes. Some studies have expressed that mothers with gestational diabetes were at increased risk for preterm labor and birth of premature neonate [17], it was the same as other studies. It should be known that copper, zinc, selenium, iron are essential components of enzymes such as glutathione peroxidase, Cu / Fe cytochrome C oxidase, or different types of superoxide dismutases and all of them are important in the body's antioxidant defense. On the other hand, these elements are also involved in glucose metabolism [11].

Zinc is mentioned as an important element for the synthesis of insulin hexamer and reducing the severity of insulin resistance and diabetes [18]. There is evidence of an increased need for zinc during pregnancy. Mishu reported a significant difference between zinc levels in women with gestational diabetes and the control group [19]. Nevertheless, in our study, serum zinc levels in mothers with gestational diabetes were higher than in the control group mothers, but this difference was not significant. Moghadam and colleagues also did not observe a significant relation between zinc levels and gestational diabetes [20]. The results of our research, despite the larger sample size, were consistent with the study of Hamdan. They also did not report a significant correlation between zinc levels in women with gestational diabetes and non-diabetic. But, the remarkable point in their study was that the two groups were well matched in terms of maternal age, parity, gestational age, and hemoglobin and body mass index [21]. Our results are the same as others in Iranian studies. Chromium is also a micronutrient that has played a key role in carbohydrate metabolism and has been mentioned as a stimulator of insulin production signals. In the study of Akhlaghi and his colleagues, like ours, the level of chromium in mothers with gestational diabetes was lower than the control group. But the results did not show a significant relation between the levels of this micronutrient in the case and control groups [11]. Numerous evidences demonstrate that serum selenium levels decrease during pregnancy [22,23]. But the results of investigations on the association between selenium levels and gestational diabetes are contradictory [24]. Some studies have shown that women with gestational diabetes have lower serum selenium levels than non-diabetic pregnant women [8,25]. However Bleys showed that serum selenium levels in people with diabetes were higher than control group, therefore, in population such as the US with sufficient serum selenium levels, selenium supplementation was not recommended to prevent primary or secondary diabetes [26]. It seems that the results of our study are consistent with it and in our society, the serum level of selenium in diabetic women is higher than non-diabetics. This is also true in another research conducted in Iran [11], but to generalize this issue, investigations with a larger sample size are required. Contradictory, in a systematic review which was performed in 2014 serum selenium concentrations were significantly lower in women with gestational diabetes than in the non-diabetic group, but did not show a cause-and-effect relation between selenium levels and gestational diabetes [24]. Although Liu and colleagues found selenium deficiency to be common among Chinese women, their findings suggested that low levels of selenium in early pregnancy was not a strong risk factor for gestational diabetes and preterm birth [27]. Copper is another element in the body that is essential for normal human physiology and the function of 30 proteins involved in metabolism, including superoxide dismutase, ceruloplasmin, and cytochrome c oxidase and dopamine beta-hydroxylase [28]. In the meta-analysis of Qiu, Serum copper levels were higher in diabetic patients than in healthy individuals [29]. In our study, serum copper levels were higher in mothers with gestational diabetes than in non-diabetic mothers and was in agreement with the study of Li et al ,but in their study, this difference was significant, which may be related to its larger sample size [9]. One of the limitations of our research was that dietary information for pregnant mothers in both groups was not available so that we could analyze the relation between nutritional factors and plasma micronutrient levels.

This study indicated that the levels of micronutrients such as zinc, copper, chromium and selenium in the two groups of diabetic and non-diabetic pregnant mothers were not significantly different. Which is the same as other studies in Iranian population, it may probably be due to diet, race, and other unknown cause, so it seems that studies with a larger sample size and multicenter along with a detailed evaluate of mother's diet is needed to generalize this issue in our society, and then the use of supplements containing these micronutrients during pregnancy should be reconsidered.

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