Cross-sectional and longitudinal evaluation of uterine artery Doppler velocimetry for the prediction of pre-eclampsia in normotensive women with specific risk factors.

OBJECTIVE

To evaluate the performance, in the prediction of pre-eclampsia, of (1) an abnormal mean uterine artery resistance index (RI; cross-sectional index) at 24 weeks of gestation, (2) the individual longitudinal flow pattern of results observed at 16, 20 and 24 weeks of gestation and (3) a multiple logistic regression model including the individual longitudinal flow pattern and the mean RI at 24 weeks.

METHODS

A total of 144 normotensive pregnant women with risk factors for pre-eclampsia were evaluated with uterine artery color Doppler at 16, 20 and 24 weeks' gestation. The following indices were obtained: (1) cross-sectional index: the mean RI of both uterine arteries at 24 weeks' gestation was calculated for each patient and considered abnormal when >/= 0.58; (2) longitudinal indices: the individual longitudinal flow pattern of mean RI of both the main uterine arteries at 16, 20 and 24 weeks' gestation was derived for each subject and defined as (a) the typical physiological flow pattern, with a trend of decrease in values or (b) the non-physiological flow pattern. The probability of having a pregnancy complicated by pre-eclampsia was also calculated by means of a multivariate logit model. The log-odds was modeled as a function of variables related to maternal characteristics, the individual longitudinal flow pattern indicator, and of the mean RI at 24 weeks' gestation as a continuous variable.

RESULTS

Pregnancies had a physiological course in 108 (75%) women, while 36 (25%) women developed pre-eclampsia during the third trimester. For the prediction of pre-eclampsia, the use of an abnormal uterine artery RI index (> or = 0.58) at 24 weeks showed a sensitivity of 77.8%, a specificity of 67.6%, a positive predictive value (PPV) of 44.4% and a negative predictive value (NPV) of 90.1%, with a likelihood ratio (LR) for an abnormal test of 2.4; with the longitudinal flow pattern indicator, sensitivity was 88.9%, specificity 82.4%, PPV 62.7% and NPV 95.7%, with a LR for an abnormal test of 4.9; the use of a logit model yielded a sensitivity of 72.2%, a specificity of 90.7%, a PPV of 72.2% and a NPV of 90.7%, with a LR for an abnormal test of 8.0.

CONCLUSIONS

In this study the use of an individual longitudinal flow pattern indicator resulted in improving accuracy in the prediction of pre-eclampsia as compared with the traditional cross-sectional mean RI at 24 weeks. A further increase in specificity and PPV was obtained using a logit model that includes the longitudinal flow pattern indicator and the cross-sectional RI at 24 weeks. Since both the longitudinal flow pattern indicator and the logit model showed a high performance in predicting pre-eclampsia in women with risk factors for impaired placentation, they might be used to identify a high-risk population in which preventive measures and/or therapeutic options might be tested.