Difference of fetal heart rate accelerations based on 10 and 15 beats per minute

To evaluate the correlation of 10 b.p.m.-10 s and 15 b.p.m.-15 s fetal heart rate (FHR) accelerations in gestations before or after 32 weeks using computerized analysis.

A combination of amplitude and duration of FHR accelerations, 10 b.p.m.-10 s (Acc10-10) and 15 b.p.m.-15 s (Acc15-15), was analyzed according to gestational weeks between January 1999 and December 2005 in 2358 normal pregnant women who received a non-stress test at 30-42 gestational weeks. A linear regression model between Acc10-10 and Acc15-15 was estimated, and the duration difference between 10 b.p.m. and 15 b.p.m. was converted into seconds.

Before 32 weeks of gestation, the mean number of FHR accelerations based on 15 b.p.m. was below 2.00 (mean + or - standard error, 1.58 + or - 0.19). The correlation between Acc10-10 and Acc15-15 was Acc15-15 + 2.8 = Acc10-10 (r(2) = 0.94, P = 0.0013). The mean duration difference between 10 b.p.m. and 15 b.p.m. was 36.8 s (range, 4-227 s).

Our study verified the difference of Acc10-10 and Acc15-15 using computerized analysis as the base of visual interpretation of the definition of FHR acceleration. Acc15-15 did not occur often enough to be relevant to the definition of FHR acceleration before 32 weeks' gestation. The difference between the mean number of FHR accelerations based on 10 b.p.m. and 15 b.p.m. within a 20-min window was 2.8.