To report the number of participants needed to recruit per baby born to trial staff during AVERT, a large international trial on acute stroke, and to describe trial management consequences.Retrospective observational analysis.56 acute stroke hospitals in eight countries.1074 trial physiotherapists, nurses, and other clinicians.Number of babies born during trial recruitment per trial participant recruited.With 198 site recruitment years and 2104 patients recruited during AVERT, 120 babies were born to trial staff. Births led to an estimated 10% loss in time to achieve recruitment. Parental leave was linked to six trial site closures. The number of participants needed to recruit per baby born was 17.5 (95% confidence interval 14.7 to 21.0); additional trial costs associated with each birth were estimated at 5736 Australian dollars on average.The staff absences registered in AVERT owing to parental leave led to delayed trial recruitment and increased costs, and should be considered by trial investigators when planning research and estimating budgets. However, the celebration of new life became a highlight of the annual AVERT collaborators' meetings and helped maintain a cohesive collaborative group.Australian New Zealand Clinical Trials Registry no 12606000185561.Participation in a rehabilitation trial does not guarantee successful reproductive activity.