What is the recommended approach for assessing clinical pelvimetry in a patient with a history of previous pregnancies, births, or pelvic surgeries?

Clinical Pelvimetry Assessment

Clinical pelvimetry has no proven role in modern obstetric practice and should not be performed routinely. The evidence demonstrates that X-ray pelvimetry increases cesarean section rates without improving perinatal outcomes, and clinical examination of pelvic dimensions does not reliably predict labor success 1.

Why Pelvimetry Is Not Recommended

• X-ray pelvimetry increases cesarean delivery rates (RR 1.34,95% CI 1.19-1.52) without reducing perinatal mortality or morbidity 1
• No reduction in adverse outcomes: Perinatal mortality (RR 0.53,95% CI 0.19-1.45), perinatal asphyxia, and NICU admissions show no improvement with pelvimetry 1
• Pelvic measurements do not predict labor outcome: Even when inlet measurements are larger in women who deliver vaginally, the incidence of successful vaginal delivery is not related to pelvic measurements 2
• Maternal height is also non-predictive of successful vaginal delivery 2

The Only Useful Clinical Predictor

• History of previous vaginal delivery is the single most reliable predictor of successful trial of labor, far superior to any pelvimetric measurement 2

When Imaging Might Be Considered (Rare Situations)

If there is genuine clinical uncertainty in specific high-risk scenarios, modern imaging may be considered, though evidence remains limited:

MRI Pelvimetry

• MRI-based pelvimetry shows stable measurements throughout the third trimester and postpartum period, suggesting pelvic dimensions do not change significantly during pregnancy 3
• 3D MRI reconstruction is technically feasible for measuring pelvic dimensions at term 4
• No radiation exposure compared to X-ray or CT methods 4
• Lacks validated predictive criteria: Even with accurate measurements, there are no established thresholds that reliably predict cephalopelvic disproportion in clinical practice 4

X-ray Pelvimetry (Historical Context Only)

• If X-ray pelvimetry is performed (which is not recommended), both lateral and anteroposterior films are necessary, as the obstetric conjugate alone is unreliable for predicting transverse inlet diameter 2
• Most valuable only at extremes: X-ray pelvimetry may identify either a clearly normal pelvis or gross bony disproportion, but is least effective in "borderline" cases where clinical management requires an adequate trial of labor 5

Recommended Clinical Approach

Instead of pelvimetry, focus on:

• Obstetric history: Document any previous vaginal deliveries (strongest predictor of success) 2
• Previous cesarean indication: If prior cesarean was for cephalopelvic disproportion, this does not preclude successful vaginal birth in subsequent pregnancies 2
• Trial of labor: Allow adequate labor progress with appropriate monitoring rather than attempting to predict success based on measurements 1, 2
• Intrapartum assessment: Clinical progress during labor is far more informative than any antepartum pelvic measurement 2, 5

Critical Pitfalls to Avoid

• Do not use pelvimetry to deny trial of labor: Women with "borderline" measurements on pelvimetry may still achieve successful vaginal delivery 5
• Do not assume pelvic dimensions are fixed: While MRI shows relative stability, the pelvis has some capacity for accommodation during labor 3
• Do not rely on single measurements: If pelvimetry is performed despite lack of evidence, isolated measurements (such as obstetric conjugate alone) are particularly unreliable 2
• Avoid unnecessary radiation: X-ray pelvimetry exposes mother and fetus to ionizing radiation without proven benefit 1