Magnetic resonance signal characteristics of the cervix as pregnancy advances.

The objective of this study is to describe magnetic resonance (MR) signal intensity (SI) changes in the cervix during pregnancy. This is an observational cohort study of women with a history of preterm delivery. MR imaging sequences were performed every 3 to 4 weeks. Using 8 regions of interest, the SIs are quantified and analyzed with respect to gestational age. Twenty-seven MR studies were performed on a cohort of 8 women. The SIs of the external os are significantly greater than those of the internal os ( P = .035). Similarly, the SIs of the outer stroma are greater than those of the inner stroma (P = .002). As gestational age advances, the inner to outer stromal SI ratio increases, primarily because of a decreasing SI in the outer stromal layer (P = .03). The MR SIs of the cervical stromal zones display variability during pregnancy and decrease with advancing gestation.