FETAL HEART-RATE (FHR) PARAMETERS DURING FHR PATTERN-A AND PETTERN-B - A LONGITUDINAL-STUDY FROM 24 WEEKS GESTATION

Objectives To assess the differences in development of fetal heart rat e (FHR) parameters of FHR patterns (FHRP) A and B, in the second half of pregnancy and to evaluate the performance of the Sonicaid System 80 02(R) with respect to the identification of these FHR patterns. Subjec ts and methods A total of 235 computerized FHR recordings were obtaine d in 29 uncomplicated pregnancies longitudinally studied from 24 weeks ' gestation onwards. Nomograms were made of basal FHR, longterm (LTV) and short-term (STV) FHR variation during both FHRP A and B, using mul tilevel analysis. Results During gestation, basal FHR decreased in bot h FHRP A and B. LN and STV increased during FHRP B and slightly decrea sed during FHRP A near term. For both FHRP A and B, intrafetal varianc e was much smaller than the total variance, indicating intrafetal cons istency. At all gestational ages, the Sonicaid System poorly identifie d A and B patterns. This was largely due to a strong correlation of bo th LTV and STV with FHR. Correction for rate resulted in 'correct' ide ntification in more than 85% of recordings. Conclusions We provide ref erence ranges for FHR, LTV and STV during both FHRP A and B from 24 we eks' gestation onwards. During FHRP A, LTV and STV are in 50% of cases below the normal range of overall FHR variation, hampering adequate a ssessment of the fetal condition. Therefore, we stress the importance of including B patterns in the analysis. There is no physiological bac kground for the assignment of periods of low and high variation, as is done by the Sonicaid System 8002(R). However, after 30 weeks' gestati on, computerized identification of patterns A and B may be possible us ing techniques as presented in this article.