Doppler Ultrasonography A Doppler shift occurs whenever the source of an ultrasound beam is moving. The usual sources of Doppler-shifted frequencies are red blood cells. The presence of intravascular blood ﬂow, ﬂow direction, and ﬂow velocity can be determined (161). Pulsed Doppler provides ultrasonographic control over which vessels are sampled. The vascular information is provided both by the shape of the time-velocity waveform (high-or low-resistance ﬂow) and by its systolic, diastolic, and mean velocities (or Doppler frequency shifts) (162). Color ﬂow Doppler ultrasonography analyzes very low amplitude signals from an entire ultrasound tomogram; the Doppler shift is then modulated into color. This information is used to gauge generalized tissue vascularity and to guide pulsed Doppler vascular sampling of specific vessels.
The waveform in the uterine arteries in the nongravid state and in the first trimester of pregnancy shows a high-resistance (little or no diastolic ﬂow), low-velocity pattern. Conversely, a high-velocity, low-resistance signal is localized to the area of developing placentation (163–165). This pattern, seen near the endometrium, is associated with normal and abnormal intrauterine pregnancies and is termed peritrophoblastic ﬂow. Whereas transvaginal ultrasonography requires a well-developed double decidual sac (or possibly cardiac activity) to localize an intrauterine gestation, the use of Doppler techniques allows detection of an intrauterine pregnancy at an earlier date. The combined use of Doppler and two-dimensional imaging allows the differentiation of pseudogestational sacs and true intrauterine gestational sacs and the differentiation of the empty uterus sign as either the presence of an intrauterine pregnancy (normal and abnormal) or absence of an intrauterine pregnancy (with an increased risk for ectopic pregnancy) (158,166).
A similar high-velocity, low-impedance ﬂow characterizes ectopic pregnancies. The addition of Doppler to the ultrasonographic evaluation of suspected ectopic pregnancy improves diagnostic sensitivity for individual diagnoses: from 71% to 87% for ectopic pregnancy, from 24% to 59% for failed intrauterine pregnancy, and from 90% to 99% for normal intrauterine pregnancy (154,158,166). Transvaginal color Doppler ultrasonography did not increase overall detection rates (167). Magnetic resonance imaging (MRI) was studied for its possible uses in the diagnosis of ectopic pregnancy. The role of MRI in the detection of ectopic pregnancy is inconclusive. It was 96% accurate in detecting fresh hematoma associated with ectopic pregnancy. Further studies need to be done to assess its predictive value (168).
Dilation and Curettage Uterine curettage is performed when the pregnancy is confirmed to be nonviable and the location of the pregnancy cannot be determined by ultrasonography. The decision to evacuate the uterus in the presence of a positive pregnancy test must be made with caution to avoid the unintentional disruption of a viable intrauterine pregnancy. Although suction curettage traditionally was performed in the operating room, it can be accomplished under local anesthesia on an outpatient basis. Endometrial sampling methods (e.g., a Novak curettage or Pipelle endometrial sampling device) are accurate in diagnosing abnormal uterine bleeding, but their reliability for intrauterine pregnancy evacuation was not studied. These devices might miss intrauterine villi and falsely suggest the diagnosis of ectopic pregnancy.