ISUOG statement on the safe use of Doppler in the 11 to 13 +6-week fetal ultrasound examination

Ultrasound safety in early pregnancy: reduced energy setting does not compromise obstetric Doppler measurements

OBJECTIVES

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.

CONCLUSION

Reliable first-trimester Doppler data can be obtained with output energy reduced to a TIb of 0.5 or 0.1.

Transvaginal 3-d power Doppler ultrasound evaluation of the fetal brain at 10-13 weeks' gestation

The objective of this study was to measure the fetal brain volume (FBV) and vascularization and blood flow using transvaginal 3-D power Doppler (3DPD) ultrasound late in the first trimester of pregnancy. 3DPD ultrasound examinations with the VOCAL imaging analysis program were performed on 36 normal fetuses from 10-13 weeks' gestation. FBV and 3DPD indices related to the fetal brain vascularization (vascularization index [VI], flow index [FI] and vascularization flow index [VFI]) were calculated in each fetus. Intra- and interclass correlation coefficients and intra- and interobserver agreements of measurements were assessed. FBV was curvilinearly correlated well with the gestational age (R2 = 0.861, p < 0.0001). All 3-D power Doppler indices (VI, FI and VFI) showed no change at 10-13 weeks' gestation. FBV and all 3-D power Doppler indices (VI, FI and VFI) showed a correlation > 0.82, with good intra- and interobserver agreement. Our findings suggest that 3-D ultrasound is a superior means of evaluating the FBV in utero, and that 3-D power Doppler ultrasound histogram analysis may provide new information on the assessment of fetal brain perfusion.

The Safe Use of Diagnostic Ultrasound in Obstetrics and Gynecology

The diagnostic ultrasound was considered safe after the intensity threshold was known and the output intensity (Ispta) was regulated to be less than 10 mW/cm2 in diagnostic devices in Japan, and diagnostic ultrasound was thought safe in USA when both thermal index (TI) and mechanical index were less than 1.0 in the obstetrical setting. Simple B-mode machine was not concerned from the thermal reason due to its extremely low ultrasound intensity, while the exposure was recommended within 30 minutes. Diagnostic ultrasound should be used after obstetrical setting in fetal study. The TI will be higher in febrile cases than nonfebrile, and the surface temperature of transvaginal scan (TVS) probe should be lower than 41°C. Simple three-dimensional or four-dimensional ultrasound imaging without pulsed Doppler studies will be as safe as Bmode when the study is within 30 minutes, because they are composed of simple B-mode images. The spectral Doppler study was not routinely used and its exposure should be short in 11 to 13 weeks of pregnancy in the statements of WFUMB and ISUOG, because experimentally early fetal animal tissue was sensitive to the studies. The use of diagnostic ultrasound should be limited for medical purposes, but not for the entertainment or keepsake of pregnancy.

How to cite this article

Maeda K, Kurjak A. The Safe Use of Diagnostic Ultrasound in Obstetrics and Gynecology. Donald School J Ultrasound Obstet Gynecol 2012;6(3):313-317.