The effect of dilute vasopressin solution on the force needed for cervical dilatation: A randomized controlled trial

OBJECTIVE: To assess the force needed to mechanically dilate the cervix of a nonpregnant woman after intracervically injecting dilute (0.05 U/mL) vasopressin solution. METHODS: In a randomized, double-blind study, equal amounts of either a dilute vasopressin solution or placebo (normal saline) were injected into the intracervical stroma at 4- and 8-o'clock positions, just beneath the mucosal surface, in 52 women immediately before cervical dilatation in preparation for operative hysteroscopy. When vasopressin solution was used, 20 mL of a dilute solution (4 U of 0.05 U/mL of vasopressin in 80 mL of normal saline) was injected. An electronic strain gauge and load cell were used to measure the peak linear force needed to dilate the cervix from 3 mm to 11 mm, using half-size metal dilators. RESULTS: The mean (+/- standard error of the mean) total peak linear force needed to dilate the cervix from 3 to 11 mm in the treated (vasopressin) and control (placebo) groups was 20.29 +/- 1.22 lb (range 5.54-40.82) and 37.05 +/- 2.55 lb (range 6.11-52.2), respectively, a statistically significant difference. The mean total peak linear force needed to dilate the cervix in the treated group and in the control group in 0.5-mm increments from 3 to 11 mm was 1.14 +/- 0.07 lb (range 0.81-1.69) and 2.08 +/- 0.07 lb (range 1.64-2.43), respectively, also a statistically significant difference. With increasing parity, significantly less force was needed to dilate the cervix from 3 to 11 mm in the treated group than in the control group (P < .001). CONCLUSIONS: Administration of dilute vasopressin solution (0.05 U/mL) to the cervical stroma significantly reduces the force needed to dilate the cervix.