Observations on the epidemiology of post partum mental illness.

This study is based on a sample of 35,486 consecutive confinements in Cardiff (1965-72) which gave rise to 67 cases of post partum mental illness. No difference was found between these cases and all resident Cardiff maternities for the same period in respect of social class, maternal parity, weight gain in pregnancy, length of gestation, birth weight, and sex of infant. A statistically significant cyclic variation in month of conception and date of birth was found with a peak frequency among conceptions in the first quarter of the year. The bearing this finding may have on the prevention of post partum mental illness and the implications of the observation that post partum mental illness and the functional psychoses have a remarkably similar temporal behaviour are discussed.