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The effect of oral evening primrose oil on bishop score and cervical length among term gravidas

      Objective

      To determine if treatment with Evening Primrose Oil (EPO) at a dose of 1 capsule given thrice daily for 1 week shows a greater effect on Bishop score by internal examination and cervical length on transvaginal ultrasound compared to placebo among term gravidas awaiting onset of labor.

      Study design

      Randomized double-blind, placebo-controlled clinical trial.

      Results

      Among seventy-one subjects who completed the study, there was a significant improvement in Bishop score in the EPO group with a mean difference of 3.68 ± 1.57 compared to 1.51 ± 1.58 for placebo (p=0.0001). Also, there was a significant reduction in cervical length with a mean difference of 0.89 ± 0.63 in the EPO group (n=38) compared to a mean of 0.42 ± 0.31 in the placebo group (n=33) (p=0.001). Pre and post-treatment Modified Biophysical profile and non-stress test were normal for all fetuses studied. Substratification analysis for parity and age of gestation showed greater impact on nulliparas and those >39 weeks age of gestation. There was no significant difference in the interval from onset or end of treatment to onset of labor between the two groups. The use of oxytocin was similar in both groups (50% in EPO and 49% in placebo group). Significantly more patients delivered vaginally in the EPO group (70% versus 51%). There was no significant difference in the birthweights of the neonates when comparing EPO and placebo group.

      Conclusion

      Evening Primrose Oil given 1 capsule thrice daily for 1 week has a significant effect in Bishop score and cervical length by transvaginal ultrasound compared to placebo and there was no effect on fetal safety profile monitored by modified biophysical profile and non-stress test. Its use as a cervical priming agent to enhance success rate for vaginal delivery may be considered for healthy term gravidas awaiting onset of labor.