Evaluation of autonomic status during three trimesters of pregnancy

Background: During pregnancy many organ systems of women undergo several adaptations in order to accommodate physiological demands of the growing foetus. Role of autonomic nervous system has been proposed for adaptation of blood circulation to meet requirements of pregnancy. Response of autonomic nervous system may vary during different stages of pregnancy. Objective: The aim of the study was to compare autonomic status of pregnant and non-pregnant females and observe changes in autonomic functions during the three trimesters of pregnancy. Material and Method: The study was conducted on 120 subjects, 90 pregnant (30 from each trimester of pregnancy) and 30 non-pregnant healthy volunteers. Batteries of non-invasive cardiovascular reflex tests providing information about sympathetic and parasympathetic autonomic nervous system were used for the assessment of autonomic status. Result: On comparing pregnant females with study group (30 from each trimester), evidence of increased sympathetic and decreased parasympathetic tone was obtained. Increase in resting heart rate and systolic blood pressure was noted to be maximum and statistically significant in 3rd trimester of pregnancy in comparison to controls, indicating increased sympathetic tone during pregnancy. The decreased parasympathetic tone in study group was indicated by lesser heart rate variability and decreased E:I ratio and 30:15 ratio. The cardiovascular response to sustained handgrip test and cold pressor test was found to be blunted in the study group indicating a decrease in total peripheral resistance. Conclusion: We conclude that marked adaptive changes take place in cardiovascular and autonomic nervous system during different trimester of pregnancy in order to meet the physiological demands of the foetus and maintaining maternal cardiovascular integrity.