Introduction
Iron deficiency (ID) is one of the most common nutritional deficiencies, especially among pregnant women and children1. Pregnant women are likely to develop ID and ID anemia2. This is due to increased iron requirement following the enlargement of blood volume, which is increased during the pregnancy to maintain physiological metabolism of maternal tissues and to meet the needs of the fetus3. Iron nutrition has a profound influence on brain development and neurotransmitter formation during fetal development. The most striking effect of ID is the impairment of intellectual function4. ID can disrupt the brain development and lead to abnormal hippocampal structure and function; it also changes brain energy metabolism and neuronal signaling4-6. Therefore, early detection of ID and iron supplementation therapy are particularly important. Given that ID often leads to pregnant complications and affects the development of offspring, iron nutrition and anemia status in pregnant women have long been the focus of research.
Iron is an essential trace element in human body and plays an important role in the function of all cells, particularly in oxygen delivery and enzymatic activity7. As mentioned above, pregnant women require more iron nutrition than non-pregnant women, indicating that ID is one of the most common nutritional problems during pregnancy3. ID is the most common cause of anemia in developing countries8. With the enlargement of blood volume, pregnant women need more iron, especially those in the second trimester of pregnancy, than non-pregnant women3. Physiologically, the development of ID can be divided into three stages, depletion of iron stores, iron depletion erythropoiesis without anemia, and iron deficiency anemia9. Because the symptoms of the first two stages are often not obvious, people tend to overlook the effect of ID, which can easily develop ID anemia. Serum ferritin (SF) is one of the most important clinical indicators of ID and can reflect iron reserves in the body4. SF is a highly sensitive and specific biochemical marker for ID, because SF levels begin to decline before the onset of ID dysfunction.
Thyroid dysfunction is a common complication in pregnant women. The prevalence of subclinical hypothyroidism in pregnant women varies from 4% to 17%, and the positive rate of anti-thyroid peroxidase (anti-TPO) antibody in pregnancy varies from 5.1% to 12.4%10. Thyroid hormones play crucial roles in the process of human growth and development, especially in the early stage of brain development11. Previous human case reports have indicated that children are at high risk of severe physical and mental handicaps or problems if their mothers have severe hypothyroidism12. These studies highlight the value of maternal thyroid function in pregnancy and the effects of maternal thyroid diseases on fetal development. Among all of the systems affected by thyroid hormones, the central nervous system (CNS) is prominent due to its high sensitivity to thyroid hormones during development13. The patients with thyroid dysfunction have various clinical symptoms. Excess thyroid hormone results in tachycardia, anxiety, tremor of the extremities, and weight loss14. Hypothyroidism causes dry skin, developmental retardation, hearing and speech impairment, and the most serious symptom is cretinism, which could lead to dementia, mental retardation and psychomotor disorder13, 15. In general, thyroid hormone deficiency affects CNS through following ways: reduction of progenitor expansion, delay in neuron proliferation, and decreased expression of proteins involved in synaptic plasticity13. Therefore, thyroid hormone levels during pregnancy should be of particular concern.
In recent years, some studies have indicated that ID during pregnancy may affect the level of thyroid hormones, and thyroid function may also interact with iron status16, 17. Therefore, through the investigation of thyroid hormone, iron nutrition and anemia status of women in the pregnant metaphase in Pingguo county, this paper further explores the relationship among ID, anemia and thyroid function.