Shows promise in increasing pregnancy rates, but further studies are needed In the United Kingdom, intrauterine insemination is the mainstay of fertility treatment carried out before couples embark on in vitro fertilisation. It is recommended by the National Institute for Health and Clinical Excellence (NICE) and by a recent international workshop1 for couples with mild male factor infertility, unexplained infertility, and mild endometriosis.2 Intrauterine insemination is attractive to couples who want minimal drug treatment, low costs, and fertilisation in the fallopian tube, as in natural conception. Many people who have religious or moral objections to in vitro fertilisation find intrauterine insemination acceptable, and the procedure is often provided in small local clinics that cannot support more costly and complex treatments. However, the approach to intrauterine insemination varies, and it is unclear which approach is best.1 3 Success rates vary from 5% to 70%.4 In the linked randomised controlled study (doi:10.1136/bmj.b4080), Custers and colleagues compared the effectiveness of …