Ans. is a, b and c i.e. Cervical length; Internal os; and Funneling of amniotic sac Cervical incompetence : Cervical incompetence is characterised by painlessdeg cervical dilatation in the seconddeg or early third trimesterdeg with ballooning of the amniotic sac into the vaginadeg, followed by rupture of membranes and expulsion of a usually live fetus. It usually occurs in 16 - 24 weeks. Diagnosis : History : The typical history of painless rupture of membranesdeg followed by the quick delivery of a live fetus in midtrimester is very suggestive.deg Non pregnant state : Internal os allows the passage of a No. 8 Heger's cervical dilator or Foley's catheter filled with 1 ml water without resistance.deg Premenstrual Hysterocervicography will show the typical funneling of the internal osdeg. In Pregnancy : - Transvaginal ultrasound is the ideal method to detect early incompetence. - The normal cervical length at 14 weeks is 35 - 40 mm and the internal os diameter is less than 20 mm. A cervical length less than 30 mm and an internal os diameter more than 20 mm is suggestive of cervical incompetence. - Other findings on ultrasound are funneling of the os.deg Serial scans may be necessary.