The effect of isosorbide dinitrate on uterine artery and umbilical artery flow velocity waveforms at mid-pregnancy

To study the effect of isosorbide dinitrate, a nitric oxide donor, on the maternal cardiovascular system and on uterine and umbilical artery blood flow velocities in mid-pregnancy.

Eighteen women with low-risk pregnancy at 17-24 weeks' gestation were given a single 5-mg dose of sublingual isosorbide dinitrate, a nitrovasodilator. Blood flow velocity waveforms in the ascending uterine artery and in the umbilical artery were measured by an image-directed, pulsed color Doppler ultrasound scan before and after the medication was administered. Maternal blood pressure (BP) and heart rate were also obtained.

The mean arterial BP decreased from 86 mmHg (95% confidence interval [CI] 72-99) to a nadir of 73 mmHg at 6 minutes (95% CI 61-85, P < .04). Mean maternal heart rate increased from 85 beats per minute (95% CI 80-90) to 96 beats per minute at 6 minutes (95% CI 87-105, P < .01). Mean systolic-diastolic flow velocity ratio (S/D) in the umbilical artery rapidly declined from 4.18 (95% CI 3.80-4.56), reaching a nadir of 3.12 at 6 minutes (95% CI 2.65-3.84, P < .001). The S/D in the uterine artery decreased from 4.83 (95% CI 3.99-5.56) to a nadir of 4.02 at 10 minutes (95% CI 3.41-4.63, P < .001).

Isosorbide dinitrate, a donor of nitric acid, lowers mean maternal BP and reduces the Doppler impedance in the umbilical and uterine arteries. This drug could prove to be beneficial when endothelial cell dysfunction leads to insufficient synthesis and release of endothelium-derived relaxing factor, resulting in generalized vasoconstriction and increased resistance to flow in the uteroplacental circulation.