Study objective: To assess the effect of hyoscine-N-butylbromide (HBB) as premedication on the rate of proximal tubal obstruction during hysterosalpingography (HSG).

Design: A randomized, double-blind controlled trial (Canadian Task Force classification I).

Setting: The Infertility Clinic of Songklanagarind Hospital.

Patients: One hundred and forty-six infertile women indicated for HSG investigation.

Interventions: Between May 1, 2016, and March 31, 2017, patients were assigned at random to receive either oral HBB 20 mg or placebo 30 minutes before the HSG procedure. If proximal tubal obstruction was found, participants were be assigned to undergo a second confirming HSG or laparoscopy with chromopertubation within 6 months.

Measurements and main results: The primary outcome was the rate of proximal tubal obstruction. The secondary outcome was the false-positive result of proximal tubal occlusion from HSG. Proximal tubal obstruction was found in 6 of 70 patients in the HBB group and in 16 of 71 in the placebo group. The rate of proximal tubal obstruction was significantly lower in the HBB group than in the placebo group (8.6% vs 22.5%; p = .04; absolute difference, 13.9%; 95% confidence interval [CI], 0.02-0.26; relative risk, 0.38; 95% CI, 0.16-0.92). After the second HSG or laparoscopy was performed (n = 22), the rate of false occlusion was 20% (1 of 6 patients) in the HBB group, compared with 69.2% (9 of 16 patients) in the placebo group.

Conclusion: Premedication with HBB before HSG can reduce the rate of diagnosis of proximal tubal obstruction and false occlusion.