Sonography in cervical insufficiency:

This ultrasound image of gravid uterus shows the cervix measuring 1.1 cms. in length (shortening) with dilatation (3mm.) of the internal os. The image was taken using the transvaginal route, using a Toshiba Xario ultrasound system. Dilatation with effacement of the cervix are diagnostic of cervical insufficiency. The management in this case would mean cervical cerclage.
See: Clinical aspects of cervical insufficiency (free article)
Image courtesy of Dr. Gunjan Puri, India.