Correlation between internal and external bony pelvis dimensions in nulliparous women

Abstract Purpose: The study correlates internal and external bony pelvis dimensions of the birth canal to estimate the size and proportions of the birth canal. Material and Methods: MRI (Magnetic Resonance Imaging) is used to identify the bony pelvis landmarks in 67 nulliparous women. The internal and external dimensions in the anterior-posterior and the transverse directions are calculated based on the landmarks and the correlation between them is set by means of the Pearson correlation coefficient ρ . The pelvic type estimation using the external bony pelvis dimensions is calculated. Results: In the sagittal plane in the plane of inlet, the study shows a very strong correlation between APD (anterior-posterior diameter) and COE (conjugata obstetrica externa) (ρ = 0 . 8%) and between SCIPP (sacro-coccygeal inferior pubic point line) and DSB (distance between PSA and SJ), where PSA refers to the upper edge of the pubic symphysis and SJ refers to the sacro- coccygeal joint (ρ = 0 . 93%). In the transverse plane, there is a very strong correlation between TD (transverse diameter) and the average of DTI (distance between left and right tuber ischiadicum) and DBC (distantia bicristalis) (ρ = 0 . 8%). IPA (internal pubic angle) does not correlate strongly with any of the proposed dimensions. Finally, the correct estimation of the pelvic type is shown to be 63% using only the external dimension. Conclusion: The study proves very strong correlations between the chosen internal and external pelvis dimensions in all major directions. However, the pelvic type estimation based on external dimensions is unclear.