Magnetic resonance imaging of the cervix during pregnancy: effect of gestational age and prior vaginal birth.

Objective: To investigate how gestational age and prior vaginal birth affect cervical anatomy on magnetic resonance imaging during pregnancy.

Study Design: Magnetic resonance images of the cervix were obtained in consecutive patients referred for a suspected fetal abnormality. We used an image processing protocol to measure cervical dimensions, orientation, and signal intensity. We determined how outcome variables were affected by gestational age and prior vaginal birth.

Results: Adequate images were obtained in 53 of 57 patients at 17 to 36 weeks. As gestational age increased by 12 weeks, the mean cross-sectional area of the cervical canal and cervical stroma increased 31% (95% confidence interval 0% to 73%) and 31% (95% confidence interval 11% to 55%), respectively. The normalized signal intensity of the stroma increased from 0.83 (95% confidence interval 0.81 to 0.85) at 20 weeks to 0.91 (95% confidence interval 0.88 to 0.94) at 32 weeks. None of the outcome variables were affected by prior vaginal birth.

Conclusion: Magnetic resonance imaging revealed that cross-sectional area and signal intensity of the cervical stroma increase with increasing gestational age.