In their interesting report, Thornton and colleagues provide robust data concerning the epidemiology of preeclampsia and eclampsia in Australia, 2000 through 2008. Among the main findings of this article, the authors conclude that there was a 50% decrease in the incidence of preeclampsia, with no change in the incidence of eclampsia. These figures translate to an almost double relative risk of eclampsia in women with preeclampsia in 2008 as compared to 2000.

These findings are of great interest; however, their interpretation may be ambiguous. The authors postulate that potential reasons for the declining rates of preeclampsia could be better antenatal care with earlier initiation of medication and an increase in induced labors and elective cesarean sections. However, they suggest no possible explanation for the stability of incidence of eclampsia.

It has been proposed that preeclampsia is a heterogeneous disorder that may be divided into 2 distinct entities, early-onset and late-onset preeclampsia, with different etiology, pathophysiology, and gestational age occurrence. We suggest that the overall decrease in the incidence of preeclampsia during 2000 through 2008 could be mainly attributed to a decline in late-onset preeclampsia rate, due to the aforementioned interventions, whereas early-onset preeclampsia, which responds poorly to therapeutic maneuvers, remained essentially stable. That is, eclampsia incidence has most likely remained unchanged, since it is primarily associated with early-onset preeclampsia.

The above hypothesis is supported by the results depicted in Table 2 of Thornton et al : in this dataset, women with preeclampsia without eclampsia are younger, deliver earlier, and are more often primiparous, in comparison with those who are nonhypertensive (mean age 29.5 vs 30.2 years; mean gestational age at delivery 37.9 vs 39.1 weeks; and proportion of primipara 45.0% vs 41.6%, respectively), whereas the latter values are even lower in women with eclampsia (28.7 years, 37.6 weeks, and 73.2%, respectively). The eclampsia odds ratio of a primiparous woman, compared with a multiparous woman, was 4.5, and the corresponding odds ratio in 2008 compared with 2000 was almost double, although not reaching statistical significance. Several researchers have reported that preeclampsia rates have increased more over time among younger than older women.

Provision of detailed trends of rates of preeclampsia and eclampsia by maternal age and gestational week of onset by the authors and a separate trend analysis of early-onset and late-onset preeclampsia could strengthen or weaken our speculation and contribute to a more comprehensive interpretation of their results.