In 2013-2014 we undertook a randomised controlled trial (RCT) to determine whether the daily ingestion of dark chocolate during pregnancy could reduce the incidence of pre-eclampsia in primigravidae. However, after two years we had not succeeded in recruiting more than 3.5% of the number of participants required to answer the research question, and the trial was halted. We also reviewed the literature on this topic and found it to be limited. We report here our findings and discuss the difficulties facing researchers in this area.