A study on cardiac autonomic modulation during pregnancy by non-invasive heart rate variability measurement

Purpose: Remarkable and uncontrollable changes with modifi cation during pregnancy are connected with the autonomic control and consequently with the heart rate variability (HRV). Heart rate variability is a sum of different mechanisms and if pregnancy is a state of change, these modifi cations could be extracted from HRV analysis. Objective: To assess the effect of pregnancy on heart rate variability among pregnant mothers during fi rst trimester of pregnancy and third trimester of pregnancy. Materials and Methods: HRV was measured for 5 minutes of continuous recording of electrocardiogram (ECG) lead II, using windows based HRV analysis system variowin-HR after obtaining permission from the Institutional Review Board of Government Medical College, Bhavnagar and written consent from 30 pregnant subjects and 30 non-pregnant control subjects at autonomic function lab, Dept of Physiology, Bhavnagar. Result: Frequency domain parameters, very low frequency (VLF), low frequency (LF), high frequency (HF) and HF normalized unit (nu) were signifi cantly decreased and LF (nu) and LF/HF signifi cantly increased in pregnant subject in 3 rd trimester as compared to their 1 st trimester of pregnancy. Time Domain parameters like SDNN, RMSSD, SDSD, NN50 count, pNN50, SD1/SD2, triangular HRV index and average R-R interval were signifi cantly decreased during 3 rd trimester of pregnancy. Conclusion: The inhibition of resting parasympathetic activity or vagal blockage and an increment of the sympathetic modulation during the 3 rd third trimester of gestation in pregnancy as compared to their 1 st trimester and healthy non-pregnant subjects. Sympathovagal imbalance and abnormally low HRV may more pronounce during later stage of normal pregnancy.