Willis-Ekbom's disease (WED), formerly called restless legs syndrome, is more 
common in pregnant than in non-pregnant women, implying that the physiological 
and biochemical changes during pregnancy influence its development. During 
pregnancy, many hormone levels undergo significant changes, and some hormones 
significantly increase in activity and can interfere with other hormones. For 
example, the steroid hormone estradiol interferes with the neuroendocrine 
hormone dopamine. During pregnancy, the activity of the thyroid axis is enhanced 
to meet the increased demand for thyroid hormones during this state. Dopamine is 
a neuroendocrine hormone that diminishes the levels of thyrotropin and 
consequently of thyroxine, and one of the roles of the dopaminergic system is to 
counteract the activity of thyroid hormones. When the activity of dopamine is 
not sufficient to modulate thyroid hormones, WED may occur. Robust evidence in 
the medical literature suggests that an imbalance between thyroid hormones and 
the dopaminergic system underpins WED pathophysiology. In this article, we 
present evidence that this imbalance may also mediate transient WED during 
pregnancy. It is possible that the main hormonal alteration responsible for 
transient WED of pregnancy is the excessive modulation of dopamine release in 
the pituitary stalk by estradiol. The reduced quantities of dopamine then cause 
decreased modulation of thyrotropin, leading to enhanced thyroid axis activity 
and subsequent WED symptoms. Iron deficiency may also be a predisposing factor 
for WED during pregnancy, as it can both diminish dopamine and increase thyroid 
hormone.