Should the marriage proceed with the suitor after adultery has occurred between the engaged couple and before the marriage contract? And what is the meaning of "istibra'"?

Adultery is one of the most heinous sins and greatest major transgressions. However, Allah accepts repentance, rejoices in it, and transforms evil deeds into good ones. Repentance consists of abandoning the sin, regretting it, and resolving never to return to it, while also concealing one's sin and not publicizing it. If you both repent from the adultery that occurred, there is no impediment to your marriage after ensuring the womb is clear (istibra'), which means verifying that the womb is free of pregnancy by waiting until the woman has one menstrual period.