symptoms, and the triggers that provoke these symptoms in those with the bipolar diathesis. The genetic, anatomical and neurochemical basis of bipolar disorder is at present unknown, and is one of the most important projects in psychiatry; but is not the main concern here. The challenge and opportunity presented by the childbearing psychoses is to identify the triggers of early postpartum onset and other onset groups. Considering that these psychoses have been known for centuries, little effort has so far been made to understand the underlying biology. Research has lagged far behind other areas of medicine and psychiatry. There is a dearth of knowledge and of theories. There is evidence of heritability, both from family studies and molecular genetics. Early onset cases occur more frequently in first time mothers, but this is not true of late postpartum or pregnancy onset. There are not many other predictors. Sleep deprivation has been suggested. Inhibition of steroid sulphatase caused behavioural abnormalities in mice. A recent hypothesis, supported by collateral studies, invokes the re-awakening of auto-immunity after its suppression during pregnancy, on the model of multiple sclerosis or autoimmune thyroiditis; a related hypothesis has proposed that abnormal immune system processes (regulatory T cell biology) and consequent changes in myelinogenesis may increase postpartum psychosis risk. Aberrant steroid hormone–dependent regulation of neuronal calcium influx via extracellular matrix proteins and membrane receptors involved in responding to the cell's microenvironment might be important in conferring biological risk. Another promising lead is based on the similarity of bipolar-cycloid puerperal and menstrual psychosis; many women have had both. Late-onset puerperal psychoses, and relapses may be linked to menstruation. Since almost all reproductive onsets occur when the menstrual cycle is released from a long period of inhibition, this may be a common factor, but it can hardly explain episodes starting in the 2nd and 3rd trimesters of pregnancy. Research directions The lack of a formal diagnosis in the DSM and ICD has hindered research. Research is needed to improve the care and treatment of affected mothers, but it is of paramount importance to investigate the causes, because this can lead to long term control and elimination of the disease. The opportunities come under the heading of clinical observation, the study of the acute episode, long-term studies, epidemiology, genetics and neuroscience. In a disorder with a strong genetic element and links to the reproductive process, costly imaging, molecular-genetic and neuroendocrinological investigations will