Yes, it is generally safe to use olive oil on your belly during the 14th week of pregnancy for a massage to prevent stretch marks. Olive oil is a natural and organic option that can help keep your skin moisturized and supple, reducing the likelihood of developing stretch marks. However, it's always a good idea to consult with your healthcare provider before starting any new skincare routine during pregnancy. They can provide personalized advice based on your specific circumstances and medical history. Additionally, if you experience any skin irritation or discomfort after using olive oil, discontinue use and consult with your healthcare provider for alternative options.