Bulging amnion in premature labor: spectrum of sonographic findings.

Premature labor or vaginal bleeding in the second and third trimesters may be associated with a spectrum of sonographically definable abnormalities of the endocervical canal. Of 13 patients encountered, eight demonstrated dilatation of the entire canal, which contained fluid, placenta, and small parts in various combinations; all delivered prematurely. The other five, in whom dilatation was limited to the proximal canal, carried to term. Seven fetuses were breech and six transverse; none were cephalic. Abnormalities of the cervical canal were seen in 6.9% of patients examined over a 1 year period for bleeding in the second and third trimesters.