METHODS	Consenting women were randomly assigned to one of the following : ( 1 ) standard arm-cervix visualized , no prespecified cervical length measurement ; ( 2 ) sequential arm-3 transabdominal cervical length measurements obtained , transvaginal sonography performed if images were inadequate or if any measurement was 3 cm or less ; and ( 3 ) screening transvaginal sonography arm-3 transvaginal cervical length measurements obtained .\