Objective: Our purpose was to determine whether transvaginal Doppler auscultation is more sensitive than transabdominal auscultation for the detection of fetal heart rate in the first trimester of pregnancy.
Study design: In a prospective study 141 patients between 6 weeks and 11 weeks 6 days of gestation underwent both transvaginal and transabdominal Doppler evaluation by use of continuous-wave Doppler instruments for detection of fetal heart rate. Transvaginal ultrasonography was used as the gold standard to establish fetal cardiac activity and to help assign gestational age. The two methods of auscultation were compared for accuracy in different gestational age ranges. Sensitivities and specificities were calculated, and associations were investigated with chi 2 analysis. The direction of disagreement between modalities was tested with the McNemar chi 2 test.
Results: Transvaginal auscultation outperformed transabdominal auscultation in every gestational age range. Transvaginal Doppler auscultation performed significantly better than transabdominal Doppler auscultation at 8 weeks to 8 weeks 6 days (p < or = 0.004) and 9 weeks to 9 weeks 6 days (p < or = 0.006). In pregnancies with cardiac activity, fetal heart rate can be successfully detected transvaginally in 60.5% of pregnancies at 8 weeks to 8 weeks 6 days and in 87.5% of pregnancies at 9 weeks to 9 weeks 6 days of gestation. This compares with successful transabdominal detection rates of 22.9% and 56% at 8 and 9 weeks, respectively. As gestational age advances both methods became increasingly sensitive for the detection of fetal heart rate. The earliest fetal heart rate detected transvaginally was at 6 weeks 0 days of gestation compared with 7 weeks 0 days transabdominally. The transvaginal Doppler method was also more successful in detecting the fetal heart rate in women with a retroverted uterus (p < or = 0.01).
Conclusion: By use of continuous-wave Doppler instrumentation, transvaginal auscultation is significantly better than transabdominal auscultation in detecting fetal heart rate between 8 weeks to 8 weeks 6 days and 9 weeks to 9 weeks 6 days of gestation. Use of transvaginal auscultation has potential in the evaluation of first-trimester fetal cardiac activity.