OBJECTIVE: To evaluate whether hypertensive disorders of pregnancy (HDP) among low-risk nulliparous women expectantly managed at or after 39 weeks of gestation are associated with adverse outcomes. DESIGN: Secondary analysis of a randomised trial. SETTING: Multicentre, USA. POPULATION: Individuals in the expectantly managed group who delivered on or after 39 weeks. METHODS: Multivariable analysis to estimate adjusted relative risks (aRR) for binomial outcomes, adjusted odds ratios (aOR) for multinomial outcomes and 95% CI. MAIN OUTCOME MEASURES: Composite adverse maternal outcome including placental abruption, pulmonary oedema, postpartum haemorrhage, postpartum infection, venous thromboembolism or intensive care unit admission. Secondary outcomes included a composite of perinatal death or severe neonatal complications, mode of delivery, small and large for gestational age and neonatal intermediate or intensive unit length of stay. RESULTS: Of the 3044 women randomised to expectant management in the original trial, 2718 (89.3%) were eligible for this analysis, of whom 373 (13.7%) developed HDP. Compared with participants who remained normotensive, those who developed HDP were more likely to experience the maternal composite (12% versus 6%, aRR 1.84, 95% CI 1.33-2.54) and caesarean delivery (29% versus 23%, aOR 1.32, 95% CI 1.01-1.71). Differences between the two groups were not significantly different for the adverse perinatal composite (7% versus 5%, aRR 1.38, 95% CI 0.92-2.07) or for other secondary outcomes. CONCLUSION: Almost 14% of low-risk nulliparous individuals expectantly managed at 39 weeks developed HDP, and were more likely to experience adverse maternal outcomes compared with those who did not develop HDP. TWEETABLE ABSTRACT: Almost 14% of low-risk nulliparous individuals expectantly managed at 39 weeks developed hypertensive disorders of pregnancy, and were more likely to experience adverse maternal outcomes compared with those who did not develop hypertensive disorders.