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.