Chorea gravidarum (CG) is the term given to chorea occurring during pregnancy. This is not an etiologically or pathologically distinct morbid entity but a generic term for chorea of any cause starting during pregnancy. Chorea is an involuntary abnormal movement, characterized by abrupt, brief, nonrhythmic, nonrepetitive movement of any limb, often associated with nonpatterned facial grimaces. [1, 2, 3]
Chorea gravidarum is regarded as a syndrome rather than a specific disease entity.
Most of the more common and serious movement disorders rarely occur during reproductive years. Hence clinicians are not very familiar with chorea gravidarum. Willson and Preece (1932) found that the overall incidence of chorea gravidarum was approximately 1 case per 300 deliveries.  According to them, the first description of chorea with onset during pregnancy was made by Horstius in 1661. The condition is much more rare now. Zegart and Schwartz (1968) found that one patient had been encountered in the course of 139,000 deliveries in 3 major Philadelphia hospitals.  The decline is probably the result of a decline in rheumatic fever (RF), which was a major cause of chorea gravidarum before the use of antibiotics for streptococcal pharyngitis.
In recent times, most cases of chorea appearing during pregnancy are caused by other diseases (eg, systemic lupus erythematosus [SLE], Huntington disease). In general, about half the cases are idiopathic, with rheumatic fever and antiphospholipid syndrome (APLS) underlying most of the remainder. 
Most patients with chorea gravidarum are young; the average age is 22 years.  Almost all reported patients have been Caucasians, although this may be due to a bias in the older literature, in which the vast majority of reported cases are among European patients. Of initial attacks, 80% occur during first pregnancies, and one half start during the first trimester.  One third begin in the second trimester. Of afflicted women, 60% previously had chorea. Recurrences may occur in subsequent pregnancies, particularly if antiphospholipid syndrome is the cause. A family history of transient chorea is not unusual.
Several pathogenetic mechanisms for chorea gravidarum have been offered, but none have been proven. Willson and Preece noted that nearly 70% of their patients gave a previous history of either rheumatic fever or chorea.  Of patients who present with chorea and no apparent carditis, 20% may develop rheumatic heart disease after 20 years. Interestingly, 50% of patients with oral contraceptive-induced chorea have a past history of chorea, which in 41% of cases is of rheumatic origin. The suggestion is that estrogens and progestational hormones may sensitize dopamine receptors (presumably at a striatal level) and induce chorea in individuals who are vulnerable to this complication by virtue of preexisting pathology in the basal ganglion.
Pathologic changes found at autopsy in chorea gravidarum include perivascular degenerative changes in the caudate nucleus.
Pathology of rheumatic brain disease is of a nonspecific arteritis with endothelial swelling, perivascular lymphocytic infiltration, and petechial hemorrhages. Aschoff bodies are not present in the brain. [7, 8] These changes are evident to some extent throughout the cerebrum but are most prominent in the corpus striatum. Severe neuronal loss occurs in the caudate nucleus and putamen. The same pathologic changes have been reported for chorea gravidarum, but all those patients also had cardiac disease.  Brain tissue from patients with acute rheumatic fever with or without chorea has not been studied for the presence of antistreptococcal antibodies. Presumably, as the inflammation resolves, the chorea disappears and degenerative changes are left in small arterioles.
Several lines of evidence suggest that heightened dopamine activity occurs either by denervation hypersensitivity or by aberrant sprouting of dopamine terminals on the remaining striatal neurons. A possible relationship between chorea gravidarum and moyamoya disease has been reported in a 16-year-old pregnant patient.  The choreic movements may be caused by ischemia or enhanced dopaminergic sensitivity mediated by increased female hormones during pregnancy.
Koide et al reported that from 1994-2004, 8 patients were diagnosed with clinically definite opsoclonus-myoclonus syndrome (a movement disorder) at Tokyo Metropolitan Neurological Hospital. This rare disorder occurred during pregnancy in 25% of their cases and they raised the possibility of a susceptibility factor in pregnancy. The relationship between opsoclonus-myoclonus syndrome and pregnancy, like chorea gravidarum, remains unclear.