Evolution of linear and nonlinear fetal heart rate indices throughout pregnancy in appropriate, small for gestational...

To assess the evolution of linear and nonlinear fetal heart rate (FHR) analysis throughout pregnancy in appropriate (AGA), small for gestational age (SGA) and preterm (PTB) fetuses.

A prospective cohort study was carried out in 171 singleton pregnancies divided in three groups: AGA (n = 147), SGA (n = 13) fetuses and spontaneous PTB (n = 11). FHR was recorded with an external sensor from the 24th to the 40th week of gestation. Linear time- and frequency-domain and nonlinear FHR indices were computed on 10-min segments. Longitudinal analysis of indices throughout pregnancy was performed with generalized estimating equations, and receiver operating characteristic (ROC) curves were calculated for the prediction of SGA and PTB fetuses.

Increasing gestational age significantly affected most FHR indices, with a general increase in variability and entropy indices, and a decrease in mean FHR. The PTB group exhibited a significantly lower short-term variation, and no monotonic increase in the sympatho-vagal balance as observed in the AGA group. The SGA group exhibited higher long-term irregularity and lower short-term irregularity than the AGA group throughout gestation. In prediction of SGA and PTB, the largest areas under the ROC curves obtained were 0.76 and 0.78, respectively.

Linear and nonlinear FHR analysis provides useful information on the evolution of fetal autonomic nervous and complexity control systems throughout pregnancy, in relation with AGA, SGA and PTB fetuses, which may be helpful in clinical practice.