Effect of antenatal betamethasone on fetal heart rate short-term variability in growth restricted fetuses.

Objectives: The study aimed to evaluate the magnitude and duration of the effect of antenatal betamethasone on fetal heart rate short-term variability (STV) in growth-restricted (FGR) fetuses in comparison with appropriate-for-gestational age (AGA) fetuses.

Methods: A prospective observational study was conducted at the UMC Ljubljana between June 2023 and June 2024, including 21 FGR and 20 AGA fetuses. We measured STV before applying betamethasone and at regular intervals for seven days after the first application or until delivery. Confounding variables were fetal and maternal demographic and clinical characteristics. Analysis was done using linear regression, paired-sample t-tests and one-way and two-way analysis of variance.

Results: The increase in STV 6-12 h after the first application was significant compared to baseline in both groups (p < 0.001). STV remained significantly elevated the first 24 h after the first application in the FGR group (p=0.018) but not in the AGA group. There was no significant difference in STV between baseline and 48 and 72 h after the first application in either group. When adjusted for gestational age, STV was significantly lower in the group of FGR compared to AGA fetuses at all times of cCTG recordings (p=0.031).

Conclusions: Following the initial increase in STV after the first dose of betamethasone, STV declines and returns to levels that doesn't differ significantly from baseline after 24 h in AGA and 48 h in FGR fetuses. Longer-lasting response of FGR fetuses to betamethasone merits further investigation.