Obesity and the metabolic syndrome (MetS) are associated with an increased risk of cardiovascular disease (CVD). Data suggest that MetS may predict CVD risk better than body mass index (BMI). As well as increased CVD risk, obesity during pregnancy is associated with adverse outcomes for maternal and foetal health, including an increased risk of caesarean birth and gestational diabetes (Marchi et al., 2015). Furthermore, it remains unknown whether low levels of physical activity (PA), which are common during gestation, have an effect on these outcomes. This study aims to explore the role of PA on metabolic health during pregnancy and the associated impact on CVD risk factors. Pregnant women (n=100) will be recruited during the first or early second trimester and complete; a blood test, submaximal cardiorespiratory fitness, macrovascular function, anthropometric and habitual PA assessment. These physiological measures will be repeated at trimesters 2 and 3. The women will be phenotyped according to BMI (non-obese <30 vs obese ≥ 30 kg/m2) and MetS status according to the International Diabetes Federation criteria. Specifically subgroups will consist of; (i) metabolically unhealthy obese, (ii) metabolically unhealthy normal weight, (iii) metabolically healthy obese, (iv) metabolically healthy normal weight, which highlight individuals most at risk of disease. Postpartum visits (at 0-4 weeks and 6 months) will consist of maternal qualitative and physiological and neonatal macrovascular structural assessments. Physiological and habitual PA variables will be compared between phenotypes. It is hypothesised that metabolically unhealthy women will confer greater CVD risk factors and display low levels of PA compared to metabolically healthy subgroups.