The scope of this article was to investigate whether intercessory prayer (IP) influences the adverse outcomes of pregnancies. A double-blind, randomized clinical trial was conducted with 564 pregnant women attending a prenatal public health care service. The women were randomly assigned to an IP group or to a control group (n = 289 per group). They were simultaneously and randomly assigned to practice prayer off-site or not. The following parameters were evaluated: Apgar scores, type of delivery and birth weight. The mean age of the women was 25.1 years of age (± 7.4), and the average gestational age was 23.4 weeks (± 8.1). The average number of years of schooling for the women was 8.1 years (± 3.1). The women in the IP and control groups presented a similar number of adverse medical events with non-significant p. No significant differences were detected in the frequency of adverse outcomes in pregnant women who practiced IP and those in the control group.