For some perinatal trials, parents can be asked to make important decisions about trial participation within limited timeframes in highly stressful circumstances. This qualitative study explores the pace of decision-making for 78 parents associated with one or more of four such trials in the UK. The themes associated with rapid decisions were concern for their baby, reactions to staff, and perceptions of the benefits and risks associated with the trial. Those who took longer to decide whether or not to participate often described similar emotions to those who made rapid decisions, but their slower decisions were because more time was available, they wanted further discussion or they found the decision particularly difficult. The majority of those who made rapid decisions felt that there were no risks associated with the trial in question, in contrast to the majority of those who made slower decisions who felt there were risks. The parents did not appear to view rapid decisions as problematic. Although there was evidence of parental vulnerability in each trial context, they largely felt that they acted swiftly and responsibly in the best interests of their child in accordance with the timeframes that were set for them.