It is generally safe for pregnant women to have sex during the 20th week of pregnancy, as long as there are no complications or medical conditions that would advise against it. However, it is important to consult with a healthcare provider to ensure individual circumstances are taken into account. Some precautions that can be followed include using comfortable positions, avoiding deep penetration, and communicating any discomfort or concerns with your partner. Additionally, practicing safe sex by using condoms can help reduce the risk of infections.