Non Linear Heart Rate Variability Study During Pregnancy in Indian Women

Introduction: Adaptation of Autonomic Nervous System (ANS) in pregnancy can be suitably assessed by Heart Rate Variability (HRV). Non linear methods of HRV better quantify the chaotic dynamics of HRV. However, non linear HRV studies are not found in literature for Indian pregnant women. Aim: To investigate the adaptation of autonomic control during pregnancy based on non linear HRV analysis. Materials and Methods: Twenty five normal healthy non pregnant volunteer women and 22 pregnant women underwent various analyses of HRV following a standard sampling. Time domain and frequency domain measures as well as non linear analysis parameters of HRV were compared between same pregnant women in first and third trimester by paired Student's t-test as well as with non pregnant women as controls by unpaired Student's t-test. Results: Time domain, frequency domain and even non linear parameters of HRV showed no statistically significant differences in control group and pregnant women during first trimester. Comparison between control group and pregnant women in third trimester showed statistically significant alterations in absolute High Frequency (HF) power, Root of Mean Squared Standard Deviation (RMSSD) of RR intervals and some non linear parameters like Standard Deviation 1 (SD1) and correlation dimension D2, whereas almost all the parameters both linear and non linear showed statistically significant differences with progression of pregnancy from first to third trimester. Conclusion: Normal pregnancy is characterised by enhancement of sympathetic component and attenuation of parasympathetic component of ANS. Decrease in non linear HRV parameters suggested decreased complexity of the autonomic control system. Non linear HRV parameters were altered to a larger extent than linear HRV parameters suggesting a need to study non linear parameters while doing HRV analysis. Further longitudinal studies with large sample size are needed to generate normative data of linear and non linear HRV parameters in pregnancy.