This document discusses cervical length screening during pregnancy to prevent preterm birth. It begins by explaining that a short cervical length is a strong predictor of preterm birth, especially for women with a prior preterm birth history. Transvaginal ultrasound is described as the gold standard for accurately measuring cervical length. The document then provides steps for proper cervical length measurement and recommends assessing length between 16-24 weeks of gestation. It outlines cervical length screening guidelines for women with a prior preterm birth, which is to screen every 1-2 weeks from 16-24 weeks. The document discusses debate around universal cervical length screening and notes insufficient evidence for screening in some high-risk situations.