During pregnancy, the developing baby receives nutrients from mother via the placenta. However, in the common pregnancy complication, intrauterine growth restriction (IUGR), blood flow to the placenta and nutrient transfer are dramatically reduced. Affected babies are also at increased short term risks during labour and are at increased risk of heart disease, diabetes and raised blood pressure in adult life. Cortisol is a steroid hormone whose levels are increased by stress. Recent research has shown that high cortisol levels can alter baby‘s growth and development. If the mother is stressed during pregnancy, for example following a bereavement, her blood cortisol levels rise. Preterm labour treatments also increase cortisol in Mum‘s blood. The placenta has an inactivating enzyme to protect the baby from increased cortisol levels in Mother‘s blood. In IUGR, however, levels of this enzyme are thought to be reduced. It is not known how cortisol alters the way the placenta works. My study will investigate if cortisol alters blood flow by assessing blood vessel behaviour directly. I will also look at how cortisol alters the proteins in the placenta that move nutrients to the baby during pregnancy. Understanding how cortisol alters the function of the placenta will assist design of future treatment strategies for IUGR and ensure the safe use of steroid hormones in preterm labour.