[Sinusoidal pattern of the fetal heart rate evaluated by tentative criteria]

The sinusoidal pattern of fetal heart rate was studied with tentative criteria as follows: 1) oscillation frequency of 6cpm or less, 2) amplitude of 10bpm or more, 3) duration of 10 minutes or more, 4) uniform frequency and amplitude, 5) decreased amplitude of accompanying minor variabilities. 7 cases of sinusoidal pattern showed frequency of 2.22 to 5.17cpm and, amplitude of 6.40 to 17.76bpm. In 6 cases, coefficients of variation of frequency and amplitude were both less than 30%. In 2 cases, the sinusoidal pattern appeared at birth, and fetal outcome was normal. Five cases of the pattern observed during pregnancy showed unfavourable courses including stillbirth in 1 case, neonatal death in 1, and fetal distress in 3. The relation between mean amplitude (x) and mean frequency (y) in each cases was represented by following equations: y=4.70-0.14x and r=-0.56. The sinusoidal pattern was also recorded in the heart rate record of an hypoxic immature neonatal infant.