We read with great interest the article published by Klein et al on uterine artery Doppler screening for preeclampsia and adverse twin pregnancy outcome in the December issue of the Journal . The authors confirmed that the reference range for uterine artery Doppler pulsatility indices (PIs) are different in twins compared with singleton pregnancy and that there is a significant difference in PI between twin and singleton pregnancy. Finally, they demonstrated quite convincingly a significant association between increased PI and adverse pregnancy outcome, presumably as a consequence of impaired placental development.

Although the authors similarly demonstrated a relationship between increased mean, lowest and highest PI, and a higher risk of preeclampsia, we are concerned about the interpretation of the findings and conclusions drawn therein. In the results, the authors stated categorically that there were no significant differences in sensitivity and specificity rates between mean, lowest and highest PI, and the incidence of preeclampsia and adverse pregnancy outcome. Despite this finding, the authors went on to state in the Comment and the abstract that “to screen for preeclampsia, they observed the highest sensitivity and specificity using the highest PI.” The latter 2 statements are incongruous and should be interpreted with caution. First, that there is no significant difference between different classes of PI means that this statement is premature at best, if not inaccurate. Second, these findings are based on only 6 cases of early and 28 cases of late preeclampsia, resulting in very large confidence intervals, precluding confidence in the authors’ statements.

Indeed, our research group has published a series of papers looking at both first- and second-trimester uterine artery Doppler in screening for preeclampsia in singleton pregnancies. We demonstrated that that the screening performances of the mean, lower, and higher uterine artery Doppler PI did not differ significantly. We would suggest that there is no plausible pathophysiological reason that our findings in studies of more than 6000 singleton pregnancies should not be extrapolated to those in twin pregnancies. Indeed, our findings are confirmed by the statistical data but not the interpretation in the paper by Klein et al. We suggest that it is unlikely that the laterality of placental development and resistance uterine blood flow is of importance when using uterine artery Doppler to screen for preeclampsia in both singleton and twin pregnancies.