We have not specified a severity of peripheral oedema, nor an n-terminal pro-B-type natriuretic peptide (NTproBNP) cut off as most patients admitted to hospital in the UK have moderate to severe oedema (to the level of the knee at least),1 and all patients should have NTproBNP soon after admission to confirm or refute the diagnosis of HF—those with low levels will not have HF as the primary problem and are thus not eligible.20 Patients can be considered eligible for inclusion at any stage during their hospitalisation as long as they are deemed to require treatment with standard care. The gene discussed is NPPB; the disease is hydrops fetalis.