16 articles that met the inclusion criteria were reviewed. Meta-analysis was only possible on castor oil and date fruit. The chance of spontaneous onset of labor in was 5.760 and 2.205 times the castor oil and date groups, respectively. Moreover, the increase in bishop score in castor oil group was 2 times higher than the control group. The results of funnel plot and Egger test found no evidence of publication bias (P = 0.710).

Peganum, Sisymbrium, chamomile, and saffron were effective in cervical ripening and onset of labor. Evening primrose was effective on Bishop score, but had no effect on spontaneous onset of labor. Red raspberry leaves were not effective in spontaneous onset of labor.