
Cervical length is a better predictor for PTD after 16 weeks- prior to this it is not as useful- I would agree with your doc re: reassurance when measured >2.5 cm (not to say we worry when it is less than this)
Soundslike you are predisposed to frequent contractions- don't overhydrate yourself as it doesn't prevent PTD and a full bladder will may you contract more. Truw lbor contractions last nly 30-60 seconds- focal contractions of the uterus last alot longer and are probably what you're experiencing
good luck
wc