Aww, I understand your worry, mama. At 20 weeks, cervical measurements can vary quite a bit, and since you've already had the cerclage done, your doctor is monitoring you closely, that's the most important thing. Please do ask your obstetrician directly about what 2.8cm means for your situation, because they know your full medical history and can give you the reassurance you need. Every pregnancy is different, and only your own doctor can advise what's okay for you. Wishing you and baby all the best!