Supplementary Material for: Short-Term Effects of Dexamethasone versus Betamethasone on Ultrasonic Measures of Fetal Well-Being: Cohort from a Blinded, Randomized Trial

Introduction: Maternal corticosteroid administration for anticipated preterm birth is common; however, the corticosteroid effect on fetal ultrasound and cardiotocograph (CTG) remains contested. This study aimed to evaluate short-term ultrasound and CTG impact of (a) dexamethasone versus betamethasone (b) pooled corticosteroid effect. Methods: Substudy of blinded randomized trial of dexamethasone versus betamethasone (given <34 weeks). Umbilical artery (UA), middle cerebral artery (MCA), ductus venosus (DV), and uterine artery Doppler, myocardial performance index (MPI), biophysical profile (BPP), and CTG measured pre-corticosteroid then 1, 2, 4, and 7 days post-corticosteroid. Results: Of 47 fetuses (39 singleton; 4 dichorionic, diamniotic twins; and 4 monochorionic, diamniotic twins) in the February 2012–2013 period, 24 received dexamethasone and 23 betamethasone at average gestation 29.8 ± 2.9 weeks. Thirteen pregnancies (30%) had pre-corticosteroid fetal concerns (estimated weight <10th centile and/or abnormal UA/MCA Doppler). Few significant differences were seen post-corticosteroid: DV pulsatility index and right MPI initially decreased 15–20%, and average BPP decreased slightly on days 1–2. There were no major differential effects of dexamethasone versus betamethasone. Discussion/Conclusion: No substantive post-corticosteroid effects were seen for most ultrasound/CTG measures in fetuses with heightened preterm birth risk but predominantly normal pre-corticosteroid measures. Clinically, this suggests avoiding overreliance on individual measures for delivery decisions post-corticosteroid; equally, multiple/marked ultrasound changes suggest true pathology and not corticosteroid effect.