Influence of somatic state on cardiovascular measurements in pregnancy

Normal pregnancy causes marked changes in cardiac and haemodynamic function but there is continuing debate about the patterns of 'normal' change. We believe that this lack of consensus is in large part caused by inappropriate assessment conditions. This study aimed to assess physiological data obtained from pregnant women during multiple steady-states and during between-state changes. The study was a longitudinal characterization of apparently healthy pregnant women aged >18 years with assessments at three antenatal stages (12-16, 26-28 and 34-36 weeks) and at 12 weeks following birth. Cardiovascular and heart rate variability (HRV) measures were quantified non-invasively during a range of states including postural manoeuvre, exercise and respiratory regulation. Cardiovascular and HRV variables were influenced by pregnancy in specific ways: (1) steady-state values were influenced differently to state-change responses; (2) cardiac output (CO) increased progressively throughout pregnancy in all states except supine rest; (3) the ΔCO response to the supine-standing manoeuvre was particularly sensitive to pregnancy stage; (4) blood pressure was unaffected by pregnancy; (6) ΔCO and ΔSBP (systolic blood pressure) were enhanced from mid-pregnancy onwards; (7) ΔHRV responses to state changes were markedly and progressively influenced by pregnancy. This study indicates that cardiovascular function in pregnant women is best quantified during at least one physical state change (in particular during the supine-to-standing manoeuvre) and that assessment during supine rest is inadequate for quantifying antenatal physiological function.