From the Research
Betamethasone administration is most associated with decreased fetal heart rate variability. This corticosteroid, typically given as two 12mg intramuscular doses 24 hours apart to pregnant women at risk of preterm delivery between 24-34 weeks gestation, temporarily reduces fetal heart rate variability for approximately 48-72 hours after administration, as shown in a study published in 2019 1. This effect occurs because betamethasone crosses the placenta and affects the fetal central nervous system, temporarily altering autonomic control of the heart.
Key Findings
- A study from 1994 found that betamethasone administration results in a considerable reduction in fetal movements and FHR variation, which may be misinterpreted as deterioration of the fetal condition 2.
- Another study from 2004 found that the effects of antenatal betamethasone administration on fetal heart rate and behavior depend on gestational age, with fetuses exposed to betamethasone at 29-34 weeks gestational age showing a decrease in FHR and reduced breathing activity 3.
- A 1998 study compared the effects of betamethasone and dexamethasone on fetal heart rate variability and found that betamethasone was associated with a decrease in fetal heart rate variability, while dexamethasone was not 4.
- A 2005 study found that maternal betamethasone administration transiently abolishes the fetal diurnal rhythms of heart rate and its variation, breathing, and body movements 5.
- The most recent study from 2019 used spectral analysis on non-invasive fetal electrocardiogram recordings to describe the effect of betamethasone on fetal heart rate variability and found a decrease in FHRV parameters on day 2 compared to day 1 1.
Clinical Implications
Healthcare providers monitoring fetal heart tracings should be aware of this normal, transient effect to avoid unnecessary interventions based on decreased variability alone when betamethasone has been recently administered. Importantly, betamethasone actually increases fetal breathing movements and does not decrease fetal tone or movement; in fact, it helps accelerate fetal lung maturity, which is why it's administered in threatened preterm birth to reduce complications like respiratory distress syndrome.