This paper focuses on the contribution of measurement-related factors to the neglect of maternal health in resource allocation for programmes and in public health research. As the recent interest in maternal health has now progressed beyond the need for information primarily for the purpose of advocacy, measurement-related factors have emerged as powerful constraints on programme action. Three outstanding needs for information can be identified: first, to establish the levels and trends of specific maternal health outcomes; secondly, to identify the characteristics and determinants of health outcomes; and thirdly, to monitor and evaluate the effectiveness of programmes designed to influence health outcomes. In order to meet these needs, the emphasis placed on operational research by the current major initiatives in maternal health must be complemented by an equivalent emphasis on methodological studies. The call for improved information by international and national agencies should be made in unison with the call for action. Inadequate information is a reality that has to be faced throughout the world, but particularly in developing countries. The quality, quantity and scope of health-related data are the elements of this inadequacy and may be discussed in terms of four factors: the indicators, the data sources, the measurement techniques, and the conceptual framework. In this paper, the neglect of maternal health and the lack of information are shown to be self-reinforcing and constitute a measurement trap sprung by these four factors. Dismantling this trap has revealed a weak conceptual framework to lie at the very centre. Maternal health has tended to be conceptualized as a discrete, negative state, characterized by physical rather than social or mental manifestations, and by a narrow time-perspective focusing on pregnancy, delivery and the puerperium. The need to broaden this perspective and to develop equally broad operational definitions represent important steps forward that must be taken.