Compared to adults admitted to general medical-surgical wards, women admitted to labor and delivery services are at much lower risk of experiencing unexpected critical illness. Nonetheless, critical illness and other complications that put either the mother or fetus at risk do occur. One potential approach to prevention is to use automated early warning systems such as those used for non-pregnant adults. Predictive models using data extracted in real time from electronic records constitute the cornerstone of such systems. This article addresses several issues involved in the development of such predictive models: specification of temporal characteristics, choice of denominator, selection of outcomes for model calibration, potential uses of existing adult severity of illness scores, approaches to data processing, statistical considerations, validation, and options for instantiation. These have not been explicitly addressed in the obstetrics literature, which has focused on the use of manually assigned scores. In addition, this article provides some results from work in progress to develop two obstetric predictive models using data from 262,071 women admitted to a labor and delivery service at 15 Kaiser Permanente Northern California hospitals between 2010 and 2017.