Outcome measures
Data were stratified by CGA presence or absence on TVUS. The primary outcome was spontaneous PTB <37 weeks gestation. Secondary outcomes included the prediction of PTB by quantifiable measures of CGA when present, and the impact of CGA assessment on CL screening for the prediction of the primary outcome. Present CGA was defined as a well-demarcated hyper- or hypoechoic region lining the cervical canal, distinct in echotexture from the peripheral cervical stroma. To attempt to quantify the extent of the CGA if present, the visualized CGA was measured for visualized length (calipers parallel to the cervical canal), as well as widest and narrowest widths (calipers perpendicular to the cervical canal). Average widths were calculated from the widest and narrowest width measurements. Approximate areas of the CGA were calculated by multiplying the measured parameters, estimating an approximately rectangular CGA overlying a linear cervical canal in the sagittal view.