Study on the cephalopelvic relationship with cephalic presentation in nulliparous full-term Chinese pregnant women by MRI with three-dimensional reconstruction

MRI-based pseudo-CT sequences as a radiation-free alternative to CT for obstetric pelvimetry: a proof-of-concept study

BACKGROUND

Pelvimetry is essential in obstetrics for delivery planning. While computed tomography (CT) is the standard, magnetic resonance imaging (MRI) offers a radiation-free alternative with zero echo time (ZTE) and black bone (BB) sequences providing high bone-to-soft tissue contrast within short scan times. This proof-of-concept study evaluates the reliability of these sequences and the agreement with CT for pelvimetry in a predominantly elderly population.

METHODS

This retrospective study included 21 female patients who underwent 3-T whole-body MRI including ZTE and BB sequences and 18fluorodeoxyglucose (18F-FDG) positron emission tomography (PET)/CT with optimized low-dose whole-body CT. Obstetric conjugate diameter (OCD), interspinous diameter (ISD), and median transverse diameter (MTD) were measured by five radiologists. Intra-reader, inter-reader, and inter-technique agreement were assessed using intraclass correlation coefficient (ICC) and repeatability/reproducibility coefficients.

RESULTS

Intra-reader agreement was good regardless of diameter or reader: all ICC ≥ 0.90, repeatability ranging from ± 0.26 to ± 0.48 cm (CT), ± 0.30 to ± 0.52 cm (BB), and ± 0.29 to ± 0.67 cm (ZTE). The inter-reader agreement was good regardless of sequence: all ICC ≥ 0.88, reproducibility ranging from ± 0.39 to ± 0.42 (OCD), ± 0.26 to ± 0.51 cm (ISD), and ± 0.53 to ± 0.58 cm (MTD). ZTE and BB showed similar agreement with CT: ± 0.57 to ± 0.81 cm when including inter-reader variability; ± 0.34 to ± 0.47 cm for only intra-reader variability.

CONCLUSION

ZTE and BB sequences provided reliable measurements with good agreement with CT, for obstetric pelvimetry. Further validation in the context of pregnancy is needed.

RELEVANCE STATEMENT

MRI-based pseudo-CT sequences are a promising radiation-free alternative to CT for obstetric pelvimetry, offering the prospect of accurate, reliable measurements of pelvic diameters in pregnant women.

TRIAL REGISTRATION

The population included female patients with suspected multiple myeloma from a previous prospective oncology trial (ClinicalTrials.gov: NCT05381077).

KEY POINTS

This study explores pseudo-CT MRI sequences for radiation-free non-invasive obstetric pelvimetry. Pseudo-CT zero echo time and black bone sequences provide repeatable and reproducible measurements of pelvic diameters. Pseudo-CT MRI sequences show good inter-technique agreement with the reference CT.

Role of fetal head-circumference-to-maternal-height ratio in predicting Cesarean section for labor dystocia: prospective multicenter study

OBJECTIVE

To evaluate the relationship between the fetal head-circumference-to-maternal-height (HC/MH) ratio measured shortly before delivery and the occurrence of Cesarean section (CS) for labor dystocia.

METHODS

This was a multicenter prospective cohort study involving four tertiary maternity hospitals. An unselected cohort of women with a singleton fetus in cephalic presentation, at a gestational age beyond 36 + 0 weeks and without any contraindication for vaginal delivery, was enrolled between September 2020 and November 2021. The MH and fetal HC were measured on admission of the patient to the labor ward. The primary outcome of the study was the performance of the HC/MH ratio in the prediction of CS for labor dystocia. Women who underwent CS for any indication other than failed labor progression, including fetal distress, were excluded from the final analysis.

RESULTS

A total of 783 women were included in the study. Vaginal delivery occurred in 744 (95.0%) women and CS for labor dystocia in 39 (5.0%). CS for labor dystocia was associated with shorter MH (mean ± SD, 160.4 ± 6.6 vs 164.5 ± 6.3 cm; P < 0.001), larger fetal HC (339.6 ± 9.5 vs 330.7 ± 13.0 mm; P < 0.001) and a higher HC/MH ratio (2.12 ± 0.11 vs 2.01 ± 0.10; P < 0.001) compared with vaginal delivery. Multivariate logistic regression analysis showed that the HC/MH ratio was associated independently with CS for labor dystocia (adjusted odds ratio, 2.65 (95% CI, 1.85-3.79); P < 0.001). The HC/MH ratio had an area under the receiver-operating-characteristics curve of 0.77 and an optimal cut-off value for discriminating between vaginal delivery and CS for labor dystocia of 2.09, which was associated with a sensitivity of 0.62 (95% CI, 0.45-0.77), specificity of 0.79 (95% CI, 0.76-0.82), positive predictive value of 0.13 (95% CI, 0.09-0.19) and negative predictive value of 0.98 (95% CI, 0.96-0.99).

CONCLUSIONS

In a large cohort of unselected pregnancies, the HC/MH ratio performed better than did fetal HC and MH alone in identifying those cases that will undergo CS for labor dystocia, albeit with moderate predictive value. The HC/MH ratio could assist in the evaluation of women at risk for CS for labor dystocia. © 2022 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Magnetic resonance imaging in late pregnancy to improve labour and delivery outcomes - a systematic literature review

BACKGROUND

Magnetic resonance imaging (MRI) provides excellent soft tissue visualisation which may be useful in late pregnancy to predict labour outcome and maternal/neonatal birth trauma.

OBJECTIVE

To study if MRI in late pregnancy can predict maternal and neonatal outcomes of labour and birth.

METHODS

Systematic review of studies that performed MRI in late pregnancy or immediately postpartum. Studies were included if they imaged maternal pelvic or neonatal structures and assessed birth outcome. Meta-analysis was not performed due to the heterogeneity of studies.

RESULTS

Eighteen studies were selected. Twelve studies explored the value of MRI pelvimetry measurement and its utility to predict cephalopelvic disproportion (CPD) and vaginal breech birth. Four explored cervical imaging in predicting time interval to birth. Two imaged women in active labour and assessed mouldability of the fetal skull. No marker of CPD had both high sensitivity and specificity for predicting labour outcome. The fetal pelvic index yielded sensitivities between 59 and 60%, and specificities between 34 to 64%. Similarly, although the sensitivity of the cephalopelvic disproportion index in predicting labour outcome was high (85%), specificity was only 56%. In women with breech presentation, MRI was demonstrated to reduce the rates of emergency caesarean section from 35 to 19%, and allowed better selection of vaginal breech birth. Live birth studies showed that the fetal head undergoes a substantial degree of moulding and deformation during cephalic vaginal birth, which is not considered during pelvimetry. There are conflicting studies on the role of MRI in cervical imaging and predicting time interval to birth.

CONCLUSION

MRI is a promising imaging modality to assess aspects of CPD, yet no current marker of CPD accurately predicts labour outcome. With advances in MRI, it is hoped that novel methods can be developed to better identify individuals at risk of obstructed or pathological labour. Its role in exploring fetal head moulding as a marker of CPD should be further explored.