Complex and irregular heart rate dynamics of anencephalic fetuses: compare to the small-for-gestational-age and fetuses with low Apgar scores

Abstract

Aim) To examine how complex and irregular fetal heart rate (FHR) dynamics differ between fetuses of normal pregnancies and those of abnormal pregnancies complicated by anencephalic, and to place this in the context of bad-outcomes pregnancies. Methods) Our study population consisted of 12 pregnant women affected by anencephalic, 120 affected by small-for-gestational-age (SGA), 120 affected by low Apgar scores, and 504 normal pregnancies as controls. We selected 504/120/120 cases of normal/SGA/low Apgar scores pregnancy that were matched to anencephalic cases ($n=12$) for maternal age (median, 28 yr, range, 24--40 yr), gestational age (36 weeks, 29--40 weeks), and mean FHR (140 bpm, 131-150 bpm). We calculated approximate entropy (ApEn), sample entropy (SampEn), short-term and long-term scaling exponents ($\alpha_1$ and $\alpha_2$) and correlation dimension (CD) to quantify irregularity and the chaotic dynamics of each FHR time series. Results) There were no significant differences in general characteristics between the anencephalic and control groups. However, fetal movements, FHR variability, FHR accelerations, the weeks at delivery, birth weight, height, 1 \& 5-min Apgar scores, ApEn, SampEn, and CD were significantly lower in the anencephalic group than in the control groups ($P<0.05$). The 2 of the anencephalic fetuses was significantly higher than that of the controls ($P<0.05$). To compare with SGA and low Apgar score group, the entropy indices in the anencephalic fetuses were not significantly lower than those of the SGA ($P > 0.05$); whereas, were significantly lower than those of the low Apgar group ($P < 0.05$). The $\alpha_2$ and CD between anencephalic and SGA fetuses were significantly different those of the SGA and low Apgar group ($P<0.05$, respectively). The entropy indices in the SGA were significantly lower than those of the low Apgar ($P < 0.05$); and, there were not significant differences in $\alpha_1$, $\alpha_2$ and CD between the SGA and low Apgar groups ($P>0.05$). Conclusion) The decreased complexity and/or irregularity in the FHR from pregnancies with anencephalic, compare to SGA and low Apgar may reflect abnormalities in the complex integrated cardiovascular control. Our data suggest that the integrity of the nervous system in the fetuses compromised by anencephalic might result directly in adverse outcomes.