Yes, it is generally safe to have sex during the 21st week of pregnancy, as long as there are no complications or medical restrictions. However, it is important to consult with your healthcare provider for personalized advice based on your specific situation. In most cases, if you have had a healthy and uncomplicated pregnancy so far, sexual activity should not pose any harm to you or your baby. It is important to communicate openly with your partner about any discomfort or concerns and listen to your body's signals. If you experience any bleeding, pain, or other unusual symptoms after intercourse, contact your healthcare provider immediately.