Heart rate variability in preterm infants and maternal smoking during pregnancy

Objective  Tobacco smoke exposure increases the risk of premature birth and of dying of sudden infant death syndrome (SIDS). Prematurity significantly increases the risk of dying of SIDS, but mechanisms underlying this epidemiological finding are unclear. The cumulated effect of both prematurity and prenatal exposure to nicotine on autonomic heart rate control has not been studied. Methods  Using coarse-graining spectral analysis, we compared heart rate variability (HRV) indices of preterm newborns at 33–34 weeks post-conceptional age from smoking (n = 19) and non-smoking (n = 21) mothers. Assessment of tobacco exposure relied on maternal reports and newborns cotinine analysis. We observed how indicators of HRV depended on gestational age at birth. Results  At 33–34 weeks postconceptional age, the newborns from smoking mothers had lower HRV low frequency power normalised to the total spectral power (LF/TP) than the control group (median values: 8% vs. 15% respectively, p < 0.02). In the non-smoking group, RR-interval values and total HRV power were correlated with gestational age at birth, with a shorter RR and a lower total HRV power in lesser gestational ages (ρ = 0.67, p = 0.03, ρ = 0.71, p = 0.003 respectively). This correlation was not observed for RR values in the group with smoking mothers.