Analysis of the difference in Fe content in the maternal fetal system
As an effective component of hemoglobin, Fe is rich in maternal blood and umbilical cord blood. The placenta is the key hub for the transfer of Fe from the mother to the fetus. The movement of Fe in the maternal fetal system is unidirectional --- from the mother to the fetus. Therefore, the level of Fe on the fetal side does not change the dynamic characteristics of Fe absorption into the placenta [8]. Studies have shown that GDM-mediated hyperglycemia can affect placental Fe homeostasis [9]. It is worth noting that there were significant differences in the content of Fe among maternal blood, placenta and umbilical cord blood in the normal group, and the average distribution characteristics of Fe in the normal group were umbilical cord blood > maternal blood > placenta (Figure. 2. A). However, there was no significant difference in Fe between maternal blood and umbilical cord blood in the GDM group, and the average distribution characteristics of Fe in the GDM group also changed: maternal blood > umbilical cord blood > placenta (Figure. 2. E). Therefore, this study suggests that the abnormal distribution of Fe content in the maternal fetal system in the GDM group may be mainly caused by the maternal side, and maternal Fe content is related to the risk of GDM [10]. The occurrence of GDM affects the barrier and transport function of the placenta with regard to Fe, thus affecting the transfer efficiency of Fe in the maternal fetal system and increasing health risk.
Fe is the producer of free radicals (FRs) (oxidants), and Fe supplementation may put people at risk of excessive intake of Fe [11]. Indeed, the chemical properties of Fe give it potential harm. This is mainly due to the key role of Fe in the Fenton reaction, which leads to the production of highly toxic hydroxyl radicals (·OH)[12]. Since free-form sub Fe ions (Fe2+) can cause the production of FR or reactive oxygen species (ROS), which can lead to peroxidation and FR chain reactions and finally to molecular damage [11]. A high Fe content will increase the risk of HDCP (e.g., PE) [10, 13]. The results of this study showed that there was a significant difference in Fe content in maternal blood, placenta and umbilical cord blood in the normal group (Figure. 2. A), but there was no significant difference in Fe content between maternal blood and umbilical cord blood in the HDCP group (Figure. 2. C). It should be noted that the content of Fe in maternal blood, placenta and umbilical cord blood in the HDCP group was higher than that in the normal group (Figure. 3. B), and the results were consistent with previous literature reports [10, 14]. With the improvement of living standards and the enhancement of people's awareness of health care, it is generally believed that the demand for Fe during pregnancy is very high, so Fe is traditionally used as a supplement during pregnancy. Although this may be correct in a few cases, most pregnant women do not need to take excessive Fe supplements[11].
Analysis of Mn content in the maternal fetal system
Mn is an important trace element in the human body. Its normal level in the body is very important for the health of the mother and fetus [15]. This study observed that the content of Mn in the placenta in different groups was significantly higher than that in maternal blood, which mainly reflected the active transport of Mn from the mother to the placenta in the maternal fetal system. It should be noted that there was a significant difference between placental Mn content in the normal group and umbilical cord blood (p < 0.05) but not in the GDM group (p > 0.05). The average content distribution of Mn in the normal group was placenta > maternal blood > umbilical blood (Figure. 2. B), while in the GDM group, it was placenta > umbilical blood > maternal blood (Figure. 2. F), thus the occurrence of GDM may affect the placental transport of Mn. In addition, there was no significant difference in Mn content between the normal group and the GDM group (Figure. 3. E), which was consistent with other research results [16-18].
Analysis of the difference in Ni content in the maternal fetal system
The placenta plays an important role in the transfer of Ni from the mother to the fetus, although the placenta provides a protective barrier against Ni toxicity [19], However, with increased pregnancy duration, the ability of the placenta to absorb and retain Ni also increases [20]. Studies have shown that in the maternal fetal system with gestational diseases, the transportation of Ni in the placenta will significantly change the morphology and permeability characteristics of the placenta during development[20]. The barrier and normal function of the placenta are damaged, as shown in Figure. 3. D, which shows that the Ni content in the cord blood of the HDCP group and GDM group was significantly higher than that of the normal group (p < 0.05). Therefore, we speculate that Ni in the HDCP group and GDM group can not only accumulate in the placenta but also damage the placental barrier function of Ni so that more Ni can pass through the placenta and enter the fetal side.
Analysis of the difference in Cr content in the maternal fetal system
Carbohydrate residues were found in the placental structure of normal and healthy pregnant women [21]. The abnormal morphology and function of the placenta in pregnant women with HDCP will lead to changes in carbohydrate morphology [22]. According to the literature, Cr is involved in the metabolism of carbohydrates and lipids [23]. The results of this study showed that the content of Cr in the placenta and umbilical cord blood in the HDCP group was significantly higher than that in the normal group (p < 0.05). The transport of Cr in the maternal fetal system may be affected by HDCP, resulting in the accumulation of Cr in the placenta, thus increasing the Cr exposure of the fetus (Figure. 3. F). Abnormal Cr content can increase the rate of spontaneous abortion, affect fetal intrauterine growth and increase the risk of adverse outcomes[24].
Analysis of Zn and Cu contents in the maternal fetal system
Zn and Cu are important trace elements in the human body and are very important for maternal health and fetal development. The results of this study show that the content and distribution of Zn and Cu in the pregnancy disease group (Figure. 1. E-F, I-J) were not significantly different from those in the normal group (Figure. 1. A-B). It can be seen that the occurrence of pregnancy diseases has no or little impact on the steady state of Zn and Cu. It has also been reported that there are a large number of enzymes containing Zn and Cu in the placenta itself[25-27]. This result can be explained.