David sent messengers and took her, and she came in to him and he lay with her (now she had just been purifying herself from her uncleanness); and she returned to her house. Bible

“now she had just been purifying herself from her uncleanness.” The Law of Moses required that a woman was unclean for seven days after her menstrual cycle ended (Lev. 15:19-33), and then she could lawfully have sex with her husband. At the end of those seven days of uncleanness she would wash herself and be clean. Bathsheba was washing herself at the end of her uncleanness. This also happens to be the time when a woman is very fertile, which seems to be the reason that this parenthesis is even in the text—it is letting the reader know that it would not have been unusual for Bathsheba to get pregnant from intercourse at that time of the month, which of course is what happened.

Commentary for: 2 Samuel 11:4