title: Foetal heart rate in early pregnancy by detection of optimally estimated displacements with pulsed Doppler signals.
abstract: Foetal heart rate (FHR) in the early stage of pregnancy can be optimally estimated by a simple system combining a conventional pulsed Doppler device with a microcomputer (CPU). The input signals for FHR have been obtained as low frequency components of foetal Doppler signals. These components are less than 50 Hz and are directly transferred from the conventional pulsed Doppler device to a microcomputer as radio-frequency signals by a specially designed I/O unit. The low frequency components have been converted into displacement signals by the continuous calculation of an arc-tangent function combined with five channel recordings from the foetal cardiac area, each separated by 2 mm on the same echo line. After selecting the optimal displacement data line, the FHR is measured by the proposed algorithm of non-parametric frequency estimation and/or the conventional autocorrelation method. The algorithm draws attention to the improved frequency selectivity by multiplication with reference signals, whose frequency is automatically optimized by the standard FHR rate determined by the length of pregnancy. The FHR determined from the displacement signals by this algorithm has provided a more optimally controlled selectivity than with the presently used autocorrelation method, especially in those pregnancies of less than 8 weeks gestation. Clinical application of this system allowed a complete 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 possible from 5 weeks 2 days by a vaginal, and 6 weeks by an abdominal procedure.
authors.affiliation: Faculty of Engineering, Gunma University, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Yamakoshi
authors.forename: M
authors.initials: M
authors.lastname: Hogaki
mesh_terms: D000465:Algorithms; D005260:Female; D006340:Heart Rate, Fetal / Q000502:physiology*; D006801:Humans; D008838:Microcomputers; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D016216:Ultrasonography, Prenatal / Q000379:methods*