Studies often use caesarean section or instrumental delivery due to obstructed
labour/dystocia as a proxy measure for obstructed labour. This is problematic, however, as
the rate in developing countries may not represent met need and the rate in developed
countries is likely to be inflated due to other factors. For example, in the United States in
the 1980s there were six times as many indications for a caesarean for cephalo-pelvic
disproportion than in Ireland for groups of women who showed the same characteristics
(nulliparity, known risk factors, age of mother and birth weight of child) and delivered in
comparable hospitals. The difference was therefore not epidemiological but due to a
subjective "cultural" factor when assessing the need for intervention.