Variability in the participants, interventions and outcomes studied is described as clinical diversity (or clinical heterogeneity) (Cochrane Handbook 9.5.1). We have now published three updates of a 2003 Cochrane review of interventions for nausea and vomiting in early pregnancy, in 2010, 2013 and 2015, with 24, 37 and 41 included studies, respectively. Here we illustrate and examine the trends in the diversity of interventions and outcomes of included studies across the reviews. There is an increasing diversity of new interventions studied (within very small trials) rather than studies of previously tested interventions, so the evidence base remains weak for any one intervention. Even where an intervention is repeatedly studied, its preparation and dose of administration may vary widely (e.g. for ginger in our review). Equally there is little consistency (of timing, instruments) in outcomes measured, leading to a proliferation of comparisons in our reviews. Our overall conclusion remains that there is little strong evidence for any one intervention to guide practice. Rather than adding small studies of new interventions, high quality sufficiently large studies of treatments already studied would assist women and clinicians. Additionally our review of outcomes measured in existing trials will form the basis for our future work to identify a core outcome set for trials of interventions for this very common condition.