On-line quantification of fetal heart rate variability.

Abstract

An on-line methods for quantification of fetal heart rate variability (FHRV) from fetal electrocardiography (FECG) is presented. A CMOS microprocessor system with a 2k read-only-memory and a 4k random-access-memory is constructed. The processor is connected to a commercial cardiotocograph, and it calculates the interval index (II) measuring the long-term variability and the differential index (DI) measuring the short-term variability of FHR. The accuracy of the system was tested by calculating the FHRV indices from simultaneously recorded direct FECG and abdominal FECG. The correlation between the results of these two methods was good. II and DI were calculated serially for 34 fetuses during normal pregnancies. The FHRV analysis succeeded in 80-100 percent of patients from the 20th until the 27th week of gestation and again from the 35th week until term. The method was less successful, 35-70 percent, between gestational weeks 28 and 34. On average, II and DI grew as the gestation advanced. II had a greater scatter than DI and it was considered to measure mainly the fetal arousal level. DI on the other hand was not below three after the 30th week of gestation. DI may become a new marker of fetal status also in antepartum fetal surveillance.