The association between increased mean arterial pressure and abnormal uterine artery resistance to blood flow during pregnancy

Objective: To examine the relation between increased mean arterial pressure (MAP) and the uterine artery resistance index (RI) to blood flow in the third trimester of pregnancy. Methods: One hundred consecutive patients in the third trimester whose pregnancies were complicated by hypertensive disorders, with or without proteinuria, had uterine artery resistance to blood flow measured using continuous-wave Doppler. Results: The RI was in the normal range in 20 patients. Unilaterally abnormal RI was found in 32 and bilaterally abnormal RI in 46 (two subjects were excluded from this categorization because measurements were obtained from only one side of the uterus). A MAP below 100 mmHg was associated with a normal RI. All six subjects with MAP of 140 mmHg or greater had bilaterally abnormal RI. Mean arterial pressure values of 100-139 mmHg included 90% of the women with normal RI, 100% of those with unilaterally abnormal RI, and 87% of those with bilaterally abnormal RI. Proteinuric and nonproteinuric groups differed with respect to both MAP (P =.04) and RI (P =.01). Pregnancy outcome was less favorable in the unilaterally abnormal RI subgroup than in the normal RI subgroup. The bilaterally abnormal subgroup of patients had the most adverse pregnancy outcomes. Conclusions: Pregnant patients in the third trimester who have increased MAP but a normal uterine artery RI can expect a good pregnancy outcome. Increased MAP associated with abnormal uterine artery RI may result in an unfavorable pregnancy outcome, particularly in those with bilaterally increased RI to blood flow. Doppler measurement of uterine artery impedance is recommended in pregnancies complicated by hypertensive disorders.