It is generally recommended to avoid sleeping on your stomach during pregnancy, especially as your belly grows. This is because lying flat on your stomach can put pressure on the uterus and restrict blood flow to the baby. However, during the early stages of pregnancy, such as at 9 weeks and 4 days, the uterus is still small enough that it may not cause harm. If you feel comfortable sleeping on your stomach and there are no complications with your pregnancy, it should be fine. As your pregnancy progresses and your belly expands, you may naturally find it uncomfortable or even impossible to sleep in this position. At that point, transitioning to sleeping on your side (preferably the left side) is recommended for better blood circulation and optimal comfort for both you and the baby. It's always best to consult with your healthcare provider for personalized advice based on your specific circumstances.