Trans-vaginal ultrasound assessment of cervical length was performed using the same machine each time Sonoace x4 (samsung Medison Co., Ltd. Seoul, South Korea) following a standardized technique in which the bladder was emptied & the vaginal probe 6.5MHz was introduced into the vagina and manipulated so that the main anatomical landmarks (bladder, fetal presentation, cervical canal, internal and external cervical os) were identified. The hyper echoic line extending from the internal os to external os, was identified by fine manipulations of the probe. The cervical canal length was measured as the distance between the internal and external os, while presence of funneling was recorded. Funneling was defined as a (V)or (U) shaped indentation of the internal os. In the presence of funneling, the length of an associated funnel was not included as part of the cervical length, and the measurement was taken from the apex of the funnel to the external os.