The ideal cervical length at 23 weeks of pregnancy is typically around 3.0-4.0 centimeters. However, it's important to note that individual variations exist, and healthcare providers may have different thresholds for concern. As for when the cervix starts to shorten, it usually occurs closer to the end of pregnancy, around 36 weeks or later. This process is known as cervical effacement and indicates that the body is preparing for labor. If you have any concerns about your cervical length or if you experience any unusual symptoms, it's best to consult with your healthcare provider for a thorough evaluation and appropriate guidance.