Drs. Lippi and Montagnana raise 2 important issues about our study of pregnant women with suspected DVT: The low specificity and positive predictive value of the D-dimer test (SimpliRED) and the relatively small number of patients with DVT (n = 13) in our cohort result in wide 95% CIs associated with the sensitivity and negative predictive value of the test.

We agree that the positive predictive value is far too low to conclude that an abnormal test result is diagnostic of DVT. The purpose of our study was to show that this D-dimer assay is sensitive and therefore has high negative predictive value, and that the specificity is sufficiently high to make the test useful. On the basis of the results, we concluded that a normal D-dimer test result can be used to exclude the diagnosis of DVT in pregnant women.

With respect to the small sample size, our calculation of the sensitivity of the D-dimer assay is based on only 13 patients with venous thromboembolism and, therefore, the corresponding CI is wide. However, the sensitivity and negative predictive value of the D-dimer assay derived from our study are consistent with the results of other studies evaluating this assay in nonpregnant patients (1–3). Nevertheless, we agree that more large, management studies are required in which further investigation and treatment for DVT are withheld when results of D-dimer testing are negative, either alone or in conjunction with a low pretest probability or normal venous ultrasonography at presentation.

The importance of evaluating D-dimer testing in pregnant women, before dismissing it as a "useless" test, cannot be overemphasized. Despite the fact that venous thromboembolism is a major preventable cause of maternal death in developed countries (4), few prospective studies have investigated the accurate diagnosis of DVT in pregnant women. The potential contribution of D-dimer testing (a noninvasive test that carries no radiation risk to the fetus) to accurately exclude DVT and, more important, pulmonary embolism should be further studied in pregnant women. Indeed, if D-dimer testing for pregnant women is abandoned without further evaluation, the "cost" to mothers and their newborns could be even greater.