Nitrous oxide versus lidocaine versus no analgesic for in-office hysteroscopy: a randomised clinical trial. - Solano Calvo JA; Del Valle Rubido C; Rodríguez-Miguel A; de Abajo FJ; Delgado Espeja JJ; González Hinojosa J; Fernández Muñoz L; Zapico Goñi Á (BJOG : an international journal of obstetrics and gynaecology, 2021)