OBJECTIVE: To explore whether the psychological response in women with an intrauterine pregnancy of uncertain viability can be modified during the waiting period to final diagnosis, by offering predictive information regarding the likely outcome of the pregnancy (chance of ongoing viability). METHODS: A single centre prospective two-arm randomized controlled trial conducted over 18 months at an inner city London teaching hospital. Consecutive eligible women attending the early pregnancy assessment unit with an interim ultrasound finding of intrauterine pregnancy of uncertain viability were recruited. All women were offered a follow-up ultrasound after 14 days. Participants were randomized to receive a prediction score for ongoing viability at 14 days or routine (control) care. Anxiety, depression and worry symptoms were assessed using validated self-report questionnaires prior to randomization and at specific time-points during the waiting period to final diagnosis. The change in psychological scores over the study time period was analysed. Secondary outcomes were the measures of perceived value of the tool reported by the participants. RESULTS: 278 women participated. No difference in the change in anxiety, depression or worry scores was demonstrated between control and intervention groups at any time point. Subgroup analysis first of women with the highest initial anxiety (HADS >11) or worry (>= 45) and second of women with the more favourable predicted prognosis (≥75% chance) showed no difference in the intervention group compared with controls. Despite this 76/110 (69%; 95% CI, 60.5-78.4%) of women who provided feedback in the intervention group reported it to be helpful and 97/110 (88.4%; 95% CI, 81.0-93.7%) reported they would use the tool again. CONCLUSIONS: Current prediction tools may be useful for healthcare professionals to guide management and optimise utilisation of early pregnancy resources. However, implementation of an accurate tool does not in this study result in an objective measurable benefit to patients in terms of reduction in anxiety, depression and worry symptoms experienced during the waiting period to final outcome compared to women who did not receive a prediction. This article is protected by copyright. All rights reserved.