title: Ultrasound safety in early pregnancy: reduced energy setting does not compromise obstetric Doppler measurements.
abstract: OBJECTIVE
  We hypothesized that first-trimester Doppler ultrasonography can be carried out at lower output energies than the currently advocated limits without compromising clinically important information.
  
  
  METHODS
  We recruited 42 pregnant women for an ultrasound examination at 12 weeks' gestation. Twenty-one women were examined with a transvaginal transducer, the rest with a transabdominal transducer. We used pulsed Doppler to measure pulsatility index (PI) and peak systolic velocity (PSV) in five clinically relevant fetal and maternal blood vessels. The energy indicator thermal index for bone (TIb) was set at 1.0, 0.5 and 0.1. Each measurement was repeated three times. A mixed linear regression model accounting for correlation between measurements was used to assess the effect of different TIb levels and transducers.
  
  
  RESULTS
  We were able to visualize the vessels by color Doppler and measure PI and PSV in all vessels at all energy levels in all the participants with the exception of the ductus venosus in two participants, yielding 1872 recordings for statistical analysis. A reduction in TIb from 1.0 to 0.5 and 0.1 had no effect on the PI or PSV values, nor was there any trend towards higher parameter variance with decreasing TIb. There was no difference between measured values of PI and PSV between the transducers, but the transabdominal technique was associated with a greater parameter variance.
  
  
  CONCLUSIONS
  Reliable first-trimester Doppler data can be obtained with output energy reduced to a TIb of 0.5 or 0.1.
authors.affiliation: Clinical Fetal Physiology Research Group, Department of Clinical Medicine, University of Bergen, Bergen, Norway. ragnar.sande@gmail.com
authors.forename: R K
authors.initials: RK
authors.lastname: Sande
authors.forename: K
authors.initials: K
authors.lastname: Matre
authors.forename: G E
authors.initials: GE
authors.lastname: Eide
authors.forename: T
authors.initials: T
authors.lastname: Kiserud
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005317:Fetal Growth Retardation / Q000209:etiology / Q000517:prevention & control*; D005318:Fetal Heart / Q000000981:diagnostic imaging / Q000528:radiation effects*; D006801:Humans; D016014:Linear Models; D015588:Observer Variation; D017410:Practice Guidelines as Topic; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011673:Pulsatile Flow; D015203:Reproducibility of Results; D016896:Treatment Outcome; D018617:Ultrasonography, Doppler, Pulsed / Q000009:adverse effects*; D016216:Ultrasonography, Prenatal / Q000009:adverse effects*