Objective: To determine the best Doppler values for differentiating ectopic pregnancy from a corpus luteum cyst of pregnancy.
Methods: This was a prospective study of 80 consecutive patients with the diagnosis of ectopic pregnancy. All ectopic pregnancies were diagnosed on the basis of the presence of an extra-ovarian adnexal mass on sonography and were confirmed surgically. The last menstrual period ranged from 4 to 11 weeks (mean, 6.3 weeks), and the maximal ectopic pregnancy diameter ranged from 0.7 to 5.5 cm (mean, 2.5 cm). Seventy-six ectopic pregnancies showed color vascularity, and 40 showed corpus luteum cysts with vascular walls. The highest peak systolic velocity and the lowest resistive index of the vascular ectopic pregnancies were compared with the corresponding values in the vascular corpus luteum cysts.
Results: The mean peak systolic velocity of the ectopic pregnancies was 35.4 cm/s compared with 28.4 cm/s in corpus luteum cysts, with no significant statistical difference (P = .1). The resistive index of the ectopic pregnancies ranged from 0.15 to 1.6 (mean +/- SD, 0.61 +/- 0.24) compared with 0.39 to 0.7 (mean, 0.52 +/- 0.10) in corpus luteum cysts, with a significant statistical difference (P = .003). In this cohort, a resistive index of less than 0.39 had a specificity of 100% and a positive predictive value of 100% for diagnosing ectopic pregnancy but was present in only 15% (confidence interval, 7%-23%) of ectopic pregnancies. A resistive index of greater than 0.7 had a specificity of 100% and a positive predictive value of 100% for diagnosing ectopic pregnancy and was present in 31% (confidence interval, 21%-41%) of ectopic pregnancies.
Conclusions: Both low and high resistive indices discriminate ectopic pregnancy from a corpus luteum cyst.