Estimating Gestational Age From Maternal-Fetal Heart Rate Coupling Parameters

Maternal and fetal heartbeat couplings are evident throughout fetal development. Most of the published work, however, did not consider maternal physiological factors such as Heart Rate Variability (HRV), and did not investigate the interrelationships of maternal-fetal coupling parameters. The aims of this study are to investigate whether: 1) maternal-fetal Heart Rate (HR) coupling ( λ-based) parameters are associated with fetal development, and 2) fetal gold standard Gestational Age (GA) can be estimated using maternal-fetal HR coupling and variability of various recording lengths. The study considered Electrocardiogram (ECG) signals from 60 healthy pregnant women with no records of fetal abnormalities. HRV and λ parameters at various Maternal:Fetal coupling ratios were calculated, and stepwise regression was utilized to create generalized linear regression models considering various lengths of recorded signals (1 and 5 min) to produce a robust estimate of fetal age. Cross-validation performances were evaluated by the mean square root of the average of squared errors (mRMSE) between age values estimated by the proposed models and gold standard GA identified by Crown-Rump Length (CRL). Effect of Fetal Behavioral States (FBSes) on proposed models with different recording lengths was considered to examine the highly nonstationary nature of signals. We found that HR coupling strength for a specific ratio is not constant throughout gestation. Results showed that ratios of 2:3 and 2:4 were common between the proposed models. The value of λ[2:3] was found to be positively correlated with GA, while λ[2:4] had a negative correlation. Compared with gold standard GA identified by CRL, the proposed regression model resulted in mRMSE of 2.67 and 3.69 weeks for the recordings of 5 and 1 min, respectively. However, when FBS was considered, both models produced lower estimation errors. Fetal GA can be more reliably estimated by a multivariate model incorporating fetal and maternal HR coupling and HRV parameters using 5 min of ECG signals.