Utilization of Heart Rate Variability for Autonomic Nervous System Assessment in Healthy Pregnant Women: A Systematic Literature Review (Preprint)

BACKGROUND Autonomic Nervous System (ANS) plays a central role in pregnancy-induced adaptations and failure in the required adaptations is associated with adverse neonatal and maternal outcomes. Mapping maternal ANS function in healthy pregnancy may help to understand ANS function. OBJECTIVE This study aimed to determine if Heart Rate Variability (HRV) has been used to assess ANS function during pregnancy, and if so whether specific HRV patterns have been identified during pregnancy representing the ANS function. METHODS Data Sources included CINAHL, PubMed, and SCOPUS databases in September 2020-June 2021. For study selection, studies that assessed HRV in healthy pregnant individuals at least once during pregnancy and/or labor, with/out comparison group (e.g., complicated pregnancy) were included. Covidence online software was used for relevancy screening. For data extraction, a narrative synthesis was applied in three steps of preliminary analysis, exploration of relationships, and assessment of the robustness of the synthesis. RESULTS Eight studies met the inclusion criteria. In 87.5% of studies, HRV was measured using ECG, and operationalized in three different ways: linear Frequency-domain (FD), linear Time-domain (TD), and non-linear methods. FD was measured in all, TD in 75%, and non-linear methods in 5% of the studies. The assessment duration varied from 5 min to 24 hours. TD indexes and most of the FD indexes decreased from first to third trimester in majority of the studies. Of FD indexes, LF (nu) and LF/ HF ratio showed ascending trend from early to late pregnancy. CONCLUSIONS We identified three HRV measuring methods along with potentially indicative HRV patterns. However, we found no justification for the selection of measurement tools, measurement timeframes, and operationalization, which threaten generalizability and reliability of pattern findings. More research is needed to determine criteria and methods for determining HRV patterns corresponding to ANS functioning in healthy pregnant persons. CLINICALTRIAL N.A.