A feasibility study of magnetic resonance pelvimetry in women of short stature to identify the risk of cephalo-pelvic disproportion

Objective

To conduct a feasibility study to assess if MR Pelvimetry can be undertaken in short stature primigravidae, with a view to a main study to answer the question ‘can MR pelvimetry be used to predict cephalo-pelvic disproportion (CPD) in women of short stature?’.

Study Design

This was a prospective single arm feasibility study. In the first phase, patient and public involvement was undertaken to assess acceptability of the study. In the second phase, primiparous women of ≤ 160 cm in height were selected from antenatal clinics. Obstetricians and midwives were asked to inform all eligible women about the study. Patients were approached in the third trimester and written information about the study provided. If the patient agreed to participate, they were invited for consent. MR scans were performed from 36 weeks gestation. Patients and their obstetricians were not informed of the results of the MR until after delivery (in view of NICE and WHO recommendations on pelvimetry).

Results

MR scans were performed on 21/35 (60%) participants who consented. The study was conducted without adverse events and was acceptable to all participants. Data were available from 19 patients; 7 (37%) of whom had caesarean section (CS) due to CPD, 7 (37%) had assisted vaginal birth (AVB), while 5 (26%) had spontaneous vaginal births (SVD). Two patients who had an elective CS were not included in the analysis. The pelvic measurements especially anatomical conjugate (inlet), transverse diameter (mid cavity) and anteroposterior diameter at the outlet were larger in the SVD group in comparison to in-labour CS /AVB. Interobserver MR scan measurements were comparable between radiologists: intraclass correlation coefficient (ICC) range 0.68 to 0.95.

Conclusion

This feasibility study suggests that conducting a full study to answer the research question ‘can MR pelvimetry predict CPD in women of short stature?’ would be feasible and acceptable to patients. The recruitment, MR scan protocol, reporting, reliability of measures were all assessed and found acceptable for a trial. A trend was observed for smaller pelvic measurements in women who needed intervention compared with those who had a natural birth/SVD. With evidence from a full trial, this could have major implications for the management of short stature women, in terms of clinical practice and safety.

Key messages

A large trial would be feasible and acceptable to assess whether MR pelvimetry can predict CPD in women of short stature. Despite the small number of patients, a trend was observed for smaller pelvic measurements in women who needed intervention compared to those who had spontaneous vaginal birth. Evidence from a large trial could help inform clinical practice, and provide information and choice for women at risk of CPD.