When a woman is 13 weeks pregnant, it is generally safe for her to engage in sexual activity unless advised otherwise by her healthcare provider. In fact, many women find that their libido increases during pregnancy. However, it is important to communicate with your partner and listen to your body's cues. If you experience any discomfort, pain, or bleeding after intercourse, it is recommended to consult with your doctor. It's also important to note that every pregnancy is different, so what may be comfortable for one woman may not be for another. As long as there are no complications or high-risk factors involved, having sex during the second trimester of pregnancy (which includes the 13-week mark) should not pose any harm to the baby. However, it's always best to consult with your healthcare provider for personalized advice based on your specific circumstances. They can provide guidance on any precautions or guidelines you should follow during this stage of pregnancy.