It is the stuff of nightmares, or a queasily dystopian film plot. A woman is undergoing a surgical procedure in a top-rated US clinic. The aim is ‘egg retrieval’, a process which collects eggs from the ovaries for use in IVF. It involves nerves and hope, long needles and pain – except the patient has been promised that the latter will be minimal, thanks to an injection of fentanyl, a powerful opioid.