The effect of antenatal steroid treatment on fetal autonomic heart rate regulation revealed by fetal magnetocardiography (fMCG).

Steroid administration to accelerate fetal lung maturation reduces neonatal morbidity and mortality in the case of preterm delivery. Behavioral observations suggest effects on fetal cardiovascular regulation.We hypothesize that beat to beat heart rate variability (fHRV) derived from fetal magnetocardiography (fMCG) will reveal a direct, acute steroidal effect on fetal autonomic heart rate regulation.Eight patients between 29 and 34 weeks of gestation at risk for preterm birth who were treated with betamethasone (2x12 mg within 24 h).Subjects were studied prior to the first and within 6 h after the second administration. Continuous fMCG was recorded with a 31-channel-SQUID biomagnetometer. Each dataset was processed by subtracting maternal cardiac artefacts and determining the time instants of the fetal heart beats. fHRV analysis was applied to periods of fetal quiescence of 4 min length.We compared fHRV prior versus post steroid administration.Steroid exposure reduced all parameters of overall fHRV significantly. The fHRV parameters representing short term variability remained unaffected. Mean fetal heart rate significantly decreased. The complexity of the heart rate patterns increased.Our results suggest an acute shift in the sympatho-vagal balance of fetuses exposed to betamethasone in utero toward sympathetic suppression.