Cervical length screening is now recommended for women with prior history of preterm bih. Between 16 and 24weeks gestation sonographic cervical measurement is completed every 2weeks. If initial or subsequent cervical length is 25 to 29mm, then a weekly interval is considered. If the cervical measurement is <25mm, cerclage is offered. Women without a history of preterm bih but with a sho cervix incidentally identified sonographically, progesterone therapy is to be offered instead of cerclage(Ref: William's Obstetrics; 25th edition)