When it comes to C4 pre-workout, the answer is no - it is not safe during pregnancy. This type of energy supplement contains high levels of caffeine and other stimulants such as taurine and guarana, which have been linked to increased heart rate and blood pressure in pregnant women. Additionally, C4 contains ingredients that are not generally recommended for pregnant women such as beta alanine and creatine monohydrate; both of which can cause dehydration, cramping or nausea when taken in large doses. Therefore, due to the potential risks associated with taking these supplements while pregnant, it is best for expectant mothers to avoid them altogether.