FETAL HEART-RATE IN EARLY-PREGNANCY BY DETECTION OF OPTIMALLY ESTIMATED DISPLACEMENTS WITH PULSED DOPPLER SIGNALS

Foetal heart rate (FHR) in the early stage of pregnancy can be optimal ly estimated by a simple system combining a conventional pulsed Dopple r device with a microcomputer (CPU). The input signals for FHR have be en obtained as low frequency components of foetal Doppler signals. The se components are less than 50 Hz and are directly transferred from th e conventional pulsed Doppler device to a microcomputer as radio-frequ ency signals by a specially designed I/O unit. The low frequency compo nents have been converted into displacement signals by the continuous calculation of an arc-tangent function combined with five channel reco rdings from the foetal cardiac area, each separated by 2 mm on the sam e echo line. After selecting the optimal displacement data line, the F HR is measured by the proposed algorithm of non-parametric frequency e stimation and/or the conventional autocorrelation method. The algorith m draws attention to the improved frequency selectivity by multiplicat ion with reference signals, whose frequency is automatically optimized by the stanard FHR rate determined by the length of pregnancy. The FH R determined from the displacement signals by this algorithm has provi ded a more optimally controlled selectivity than with the presently us ed autocorrelation method, especially in those pregnancies of less tha n 8 weeks gestation. Clinical application of this system allowed a com plete determination of foetal heart rate from 6 weeks of gestation by a transvaginal approach and from 7 weeks by transabdominal procedures. In some specific cases, with prominent foetal components, it was poss ible from 5 weeks 2 days by a vaginal, and 6 weeks by an abdominal pro cedure.