How to assess the pelvis in a pregnant patient for normal delivery?

Assessment of the Pelvis in Pregnancy for Normal Delivery

Clinical pelvimetry and traditional pelvic typology classifications (Caldwell-Moloy) should not be used to assess pelvis adequacy for vaginal delivery, as these outdated techniques lack evidence correlating pelvic measurements with obstetric outcomes and are rooted in racist methodology. 1

Why Traditional Pelvic Assessment Is Not Recommended

The historical approach to pelvic assessment for vaginal delivery has been thoroughly discredited:

• The Caldwell-Moloy classification system and clinical pelvimetry cannot reliably predict obstetric outcomes because the human pelvis varies in complex, healthy ways that these artificial typologies fail to capture 1
• These techniques were developed on biased, non-representative samples and falsely assumed that bony pelvic dimensions are the primary determinant of birth difficulty 1
• Modern evidence demonstrates that pelvic capacity is dynamic—pelvic dimensions increase significantly throughout pregnancy (from 20 to 32 weeks gestation) and change substantially with maternal positioning 2

Evidence-Based Approach to Delivery Planning

Standard Clinical Assessment

For most pregnant patients, routine pelvic measurement is unnecessary—the focus should be on identifying specific risk factors rather than attempting to predict pelvic adequacy:

• Standard obstetric ultrasound evaluation includes transabdominal assessment of the cervix during second and third trimester examinations 3
• Transvaginal ultrasound provides the most complete cervical assessment when transabdominal visualization is inadequate or shows suspicious findings 3, 4

Special Populations Requiring Cesarean Delivery

Women with skeletal dysplasia require cesarean delivery because pelvic anatomy in most cases precludes vaginal delivery—the infant's cranium will be too large to pass through the birth canal regardless of whether the infant has normal or increased head size 3

• These patients can typically undergo cesarean delivery with Pfannenstiel skin incision and low transverse uterine incision 3
• This represents the only clear scenario where maternal pelvic anatomy definitively determines delivery route 3

Dynamic Nature of Pelvic Capacity

Understanding that pelvic dimensions are not fixed is crucial:

• Pelvic capacity increases throughout pregnancy, with measurable enlargement from gestational week 20 to 32 at both pelvic inlet and outlet 2
• Maternal positioning dramatically affects pelvic dimensions: shifting from supine to kneeling squat position increases transverse diameters by 0.9-1.9 cm (7-15%), with bispinous diameter increasing from 12.6 cm to 14.5 cm in pregnant women 5
• The kneeling squat position significantly increases midplane and pelvic outlet dimensions by up to 1 cm compared to supine positioning 2

Clinical Implications

The appropriate approach is trial of labor rather than attempting to predict success based on pelvic measurements:

• Pelvic dimensions change with positioning, making static measurements clinically meaningless 5, 2
• The complexity and variability of birth physiology cannot be reduced to simple pelvic measurements 1
• Empowering pregnant patients with positioning options during labor may facilitate delivery by optimizing pelvic dimensions 5, 2

Common Pitfall to Avoid

Do not attempt manual pelvimetry or apply outdated pelvic classification systems—these provide false reassurance or unnecessary concern without improving outcomes and perpetuate harmful historical biases 1