Cardiovascular deaths remain the most common cause of pregnancy-related deaths.1 Pregnancy is a time of unique cardiovascular adaptation with maternal physiology altering through gestation to support the demands of the growing fetus. Several organs have particularly increased blood requirements during pregnancy, beside the uterus, including skin, kidneys and breasts. However, reports of the magnitude and timing of increases in cardiac output during normal pregnancy have been inconsistent. A clear understanding of how cardiac output and other haemodynamic parameters change in normal pregnancy might allow earlier and more accurate identification of maladapted cardiovascular physiology that characterises some complications in pregnancy and possibly allow attenuation of future sequelae. In particular, there has been interest in the impact of hypertensive disorders of pregnancy on cardiac function because they occur in up to 20% of pregnancies and are specifically associated with both changes in cardiac output during pregnancy, cardiac dysfunction2 and increased risks of cardiovascular diseases in later life for both mother and child.3

In their Heart publication, Meah et al4 have adopted a new methodological approach to describe changes in cardiac output during pregnancy, which has allowed them to report findings from a substantially larger dataset than previously possible. They have performed a systematic review of the literature and undertaken a series of meta-analyses on the accumulated findings of cardiac output and other haemodynamic data in healthy singleton pregnancies, from non-pregnancy through to post partum. To ensure an adequate sample size, they have had to draw on a heterogeneous source of data and include studies that report a range of modalities including echocardiography, impedance cardiography, suprasternal Doppler and inert gas rebreathing. Nevertheless, they found that this …