Clinical significance of fetal tachypnea during antepartum biophysical testing

Fetal tachypnea has been regarded as a rare finding with a poor perinatal prognosis. Eighteen cases of fetal tachypnea were noted during the biophysical tests of 200 patients. Biophysical testing consisted of concurrent ultrasound observations of fetal breathing and body movements and electronic monitoring of fetal heart rate, coupled with determinations of fetal tone and amniotic fluid volume. Fetal breathing movement frequency and rate, fetal trunkal movement frequency, and baseline fetal heart rate were analyzed on a programmed microcomputer. The mean (+/- SD) breathing rate was 68.2 +/- 6.4 breaths per minute; mean breathing frequency, 55 +/- 22.6%; mean baseline heart rate, 141 +/- 8 beats per minute; mean trunkal movement incidence, 5.5 +/- 2.6%; and mean acceleration frequency, 14.6 +/- 9.8 per hour. No fetus was apneic for more than eight minutes, and there were no significant correlations between fetal breath rates and the other biophysical parameters. There were no perinatal deaths. Seven fetuses experienced perinatal morbidity, of whom five had other abnormalities on biophysical testing. This study indicates that fetal tachypnea occurs more often than previously believed and does not generally signify fetal compromise unless other biophysical abnormalities are also present.