Methods
A group of 69 Caucasian women in uncomplicated, singleton pregnancy who voluntarily responded to our mass media invitation were eligible to participate in the study. To randomly allocate the participants into the high intensity interval training group (HIIT group) or educational intervention (EDU group) and to avoid the “contamination effect,” feasibility and ethical issues during the study implementation we used the pipeline arm-focused randomization (PAFR) model, based on the assumptions of pipeline randomization (Flow of participants through the study. HIIT, high intensity interval training; EDU, educational. 