['The aim of the present study was to examine the influence of moderate physical exercise throughout pregnancy on the duration of labor stages.', 'Study was a randomized controlled trial.', 'The study took place at Hospital Puerta de Hierro and Hospital Severo Ochoa in Madrid, Spain.', 'We examined 166 pregnant women (31.6 ± 3.8 years), and all had uncomplicated and singleton gestation. Of these 83 were allocated to the exercise group (EG) and 83 to the control group (CG).', 'Women from the EG participated in a physical conditioning program throughout pregnancy, which included 55- to 60-minute sessions, 3 days per week.', 'Pregnancy outcomes were measured: duration of labor stages, gestational age, weight gain, type of delivery, birth weight, birth size, head circumference, Apgar score, pH of umbilical cord.', "Student's unpaired t-tests and χ(2) tests were used; p values of < .05 indicated statistical significance. Cohen's d was used to determine the effect size.", "Significant differences were found in the duration of the first stage of labor (EG = 389.6 ± 347.64 minutes vs. CG = 515.72 ± 353.36 minutes; p = .02, effect size Cohen's d = .36). The second and third stages did not differ between the study groups."] Does regular Exercise Throughout Pregnancy be Associated With a Shorter First Stage of Labor?