Abstract Importance: Inadequate management of elevated BP is a significant contributing factor to maternal deaths. Self-monitoring of blood pressure (BP) in the general population has been shown to improve the diagnosis and management of hypertension, however little is known about its use in pregnancy. Objective: To determine whether self-monitoring of BP in higher risk pregnancies leads to earlier detection of pregnancy hypertension. Design, setting and participants: Unmasked, randomised clinical trial that recruited between November 2018 and October 2019. 2441 pregnant individuals at higher risk of pre-eclampsia were recruited at 20 weeks’ gestation from 15 hospital maternity units in England with final follow-up in April 2020. Interventions: Participating individuals were randomised to either BP self-monitoring with telemonitoring (n=1223) plus usual care or usual antenatal care alone (n=1218) without access to telemonitored BP. Main Outcomes: The primary outcome was time to first recorded hypertension measured by a healthcare professional. Results: Among 2441 participants who were randomized (mean age, 33; median gestation 20 weeks), 2346 (96%) completed the trial. The time from randomisation to clinic recording of hypertension was not significantly different between individuals in the self-monitoring group (mean 104 days) vs the usual care group (mean 106 days) (mean difference -1.6 days (95% confidence intervals -8.1, 4.9, p = 0.6). Eighteen serious adverse events were reported during the trial with none judged as related to the intervention: 12 (1%) in the self-monitoring group and 6 (0.5%) in those receiving usual care. Conclusions and relevance: Among pregnant individuals at higher risk of pre-eclampsia, blood pressure self-monitoring with telemonitoring compared with usual care did not lead to significantly earlier clinic-based detection of hypertension