Cervical length

Hello twin mamas! Looking for some other input from you gals. I am 21+4 today, ob appt today showed baby a pretty low in my pelvis and my cervical length right around 2.8. I will now start weekly checks to see if it's continuing to shorten, but doc thinks best rest is in my near future. Also dealing with at least a partial previa as well. Just curious how other moms are or were looking at this point in the pregnancy and what your outcomes were :)