Effect of betamethasone administration on fetal heart rate tracing: a blinded longitudinal study

Computerized fetal heart rate (FHR) analysis revealed that antenatal corticosteroids transiently suppress multiple parameters of fetal well-being, potentially leading to the erroneous diagnosis of fetal distress and to unnecessary iatrogenic delivery of premature infants. Our aim was to determine whether clinicians who visually analyze FHR tracings detect these suppressive effects, thereby potentially affecting their clinical management decisions.

Singleton pregnancies admitted for preterm labor between 26 and 34 weeks' gestation received two doses of betamethasone, 24 h apart, and were monitored daily between 16:00 and 19:00 h for 5 days. FHR tracings were randomly coded and presented in a non-consecutive order to four clinicians, who were unaware of the time of steroid administration. FHR baseline, FHR variability, number of accelerations and amplitude of maximal FHR acceleration were determined. Variability was scored semiquantitatively based on a modified Hon score. Analysis of variance (ANOVA) with repeated measures was used for primary analysis and followed up with the Wald test of significance. Corrections for multiple comparisons were made and only p < 0.005 considered significant. ANOVA was also used to assess the uniformity of trend in the interpretation by the four examiners for each given day.

Baseline FHR was elevated, FHR variability was decreased, and the number of accelerations decreased on day 1 (p < 0.0001; p < 0.0001; p < 0.0001) and day 2 (p > 0.0001; p < 0.0001; p < 0.0001) in comparison to day 0. On day 3, the FHR baseline, variability and number of accelerations returned to pre-exposure values (p = NS). The maximal amplitude of FHR accelerations showed a trend towards reduction (p = 0.08). Subgroup analysis by gestational age (group I = 26-30 weeks and group II = 30-34 weeks) showed the same response patterns and significance levels for both groups.

Betamethasone causes profound, but transient, suppression of FHR parameters, which can mimic fetal distress. This effect is clinically recognized by visual FHR analysis. Clinicians need to be aware of this phenomenon, in order to avoid unwarranted iatrogenic delivery.