Maternal cardiovascular changes from pre-pregnancy to very early pregnancy

Our aim was to assess changes in maternal cardiovascular haemodynamics, including central blood pressure (BP), wave reflections and aortic stiffness, from pre-pregnancy to very early pregnancy.

Fifty-six healthy nulliparous or women with previous uncomplicated pregnancy were studied prior to conception and in very early pregnancy. Assessments of brachial and central BPs, pulse wave reflection quantified by augmentation index (AIx), aortic stiffness using carotid femoral pulse wave velocity (aPWV) and cardiac output (CO) were performed.

Pregnancy measurements were obtained at median gestational age of 6.3 weeks [interquartile range (IQR) 6-6.5 weeks] from the last menstrual period. Whilst heart rate (HR) increased from 67  ±  10 to 71  ±  10  bpm. (P  =  0.001), brachial SBP, DBP and central SBP were all lower than the pre-pregnancy values (109  ±  10 to 104  ±  7 mmHg, 72  ±  8 to 65  ±  6 mmHg and 99  ±  10 to 92  ±  7 mmHg, respectively; P  <  0.001 for all). AIx adjusted for HR fell (19  ±  10 to 13  ±  9%; P  =  0.001) as did peripheral vascular resistance (PVR; 1234 ± 229 to 1128  ±  280 dynes/s/cm; P = 0.003). aPWV adjusted for mean arterial pressure (MAP) was unchanged (5.3  ±  0.6 to 5.1  ±  0.6m/s; P  =  0.2).

Significant changes occur in brachial and central BP, AIx and PVR in successful, ongoing pregnancies, by about 6-7 weeks gestation; much earlier than has hitherto been assumed. Using late first trimester data as 'baseline' cannot be relied on to estimate the extent of cardiovascular changes in normal pregnancy. Future studies of cardiovascular changes in pregnancy should, therefore, have a pre-pregnancy starting point.