Nitroglycerin as a uterine relaxant: a systematic review.

OBJECTIVE To evaluate the effectiveness of nitroglycerin as a uterine relaxant for preterm labour, fetal extraction at Caesarean section, external version, embryo transfer, cervical dilation for first trimester pregnancy termination, and primary dysmenorrhea. DESIGN A systematic review of randomized control trials (RCTs) of nitroglycerin in obstetrics and gynaecology. METHODS We searched PubMed (1966-2001), the Cochrane Controlled Trials Register, and the International Journal of Obstetric Anesthesia using text terms quot:nitroglycerin," "glyceryl trinitrate," "uterus," "uterine," and "relaxation." The last search was conducted in January 2001. References from review articles and abstracts from major scientific meetings (1997-2000) were reviewed for relevant publications. RCTs comparing nitroglycerin to either placebo or another therapeutic intervention (ritodrine, magnesium sulphate, and prostaglandin) and whose quality score was equal to or greater than 2 were included (Class I evidence as described in the Report of the Canadian Task Force on the Periodic Health Exam). RESULTS Sixty articles were retrieved of which 13 were RCTs. Nitroglycerin was more effective for arresting preterm labour than placebo but not more effective when compared to ritodrine or magnesium. Nitroglycerin was not superior to placebo for uterine relaxation for either fetal extraction at Caesarean section or for external version. There were no differences in ease of embryo transfers when nitroglycerin spray was compared to placebo. In first trimester pregnancy terminations, less force was required to dilate the cervix when nitroglycerin was compared to no treatment. The incidence of preeclampsia was not reduced by nitroglycerin but fewer complications were noted when compared to the placebo group. In patients with primary dysmenorrhea, nitroglycerin significantly decreased pain. CONCLUSION Although nitroglycerin is widely used, its superiority over currently used tocolytic agents is unproven. (Class C recommendation) Nitroglycerin has been demonstrated to decrease pain associated with dysmenorrhea. (Class A recommendation)