Cervix appears as a soft tissue structure with medium-level echoes
Endocervical canal appears as echogenic line (mucus plug) surrounded by hypoechoic zone of endocervical glands
Cervical length: Normal cervix is >3 centimeters in length (length of endocervical canal from the internal os to the external os)
Cervical width: Anteroposterior (AP) diameter of the cervix at the midpoint between internal and external os
Gradual cervical effacement and shortening normally begins at ~30 weeks of gestation.
In multifetal pregnancy, cervix is much shorter from 20-week gestation onward.
Widening of os and cervical length <2.5 centimeters at </= 24 weeks is s/o cervical insufficiency.
• Funneling of the internal os has been reported as an early sign (Figure 28.1).
Seen as a bulging/herniation of fetal membranes >3 millimeters into the internal os.
>50% funneling before 25 weeks is a/w >75% risk of preterm delivery.
• Shortening of cervical canal (from internal os to external os).
• Cervical canal gets dilated and in severe cases, amniotic sac may prolapse through (Figure 28.2) the cervix into vagina with or without the products of conception. (Bulging amnion).