It is generally recommended to start taking prenatal vitamins, such as pregnacare, before conception or as soon as you find out you are pregnant. These vitamins provide essential nutrients for the healthy development of your baby. While it is safe to start taking them at five weeks, it's best to consult with your healthcare provider for personalized advice. They can assess your specific needs and recommend the appropriate dosage and timing for starting prenatal supplements. Remember that a balanced diet is also crucial during pregnancy, so make sure to include a variety of nutrient-rich foods in your meals.