Determining Cervical Ripeness and Labor Outcome

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.

The role of noninvasive diagnostic imaging in monitoring pregnancy and detecting patients at risk for preterm birth: a review of quantitative approaches

Preterm birth (PTB) is the leading cause of neonatal morbidity and mortality worldwide. The ability to predict patients at risk for preterm birth remains a major health challenge. The currently available clinical diagnostics such as cervical length and fetal fibronectin may detect only up to 30% of patients who eventually experience a spontaneous preterm birth. This paper reviews ongoing efforts to improve the ability to conduct a risk assessment for preterm birth. In particular, this work focuses on quantitative methods of imaging using ultrasound-based techniques, magnetic resonance imaging, and optical imaging modalities. While ultrasound imaging is the major modality for preterm birth risk assessment, a summary of efforts to adopt other imaging modalities is also discussed to identify the technical and diagnostic limits associated with adopting them in clinical settings. We conclude the review by proposing a new approach using combined photoacoustic, ultrasound, and elastography as a potential means to better assess cervical tissue remodeling, and thus improve the detection of patients at-risk of PTB.

Magnetic Resonance Signal Characteristics of the Cervix as Pregnancy Advances

The objective of this study is to describe magnetic resonance (MR) signal intensity (SI) changes in the cervix during pregnancy. This is an observational cohort study of women with a history of preterm delivery. MR imaging sequences were performed every 3 to 4 weeks. Using 8 regions of interest, the SIs are quantified and analyzed with respect to gestational age. Twenty-seven MR studies were performed on a cohort of 8 women. The SIs of the external os are significantly greater than those of the internal os ( P = .035). Similarly, the SIs of the outer stroma are greater than those of the inner stroma (P = .002). As gestational age advances, the inner to outer stromal SI ratio increases, primarily because of a decreasing SI in the outer stromal layer (P = .03). The MR SIs of the cervical stromal zones display variability during pregnancy and decrease with advancing gestation.

Ex vivo assessment of mouse cervical remodeling through pregnancy via 23Na MRS

Preterm birth occurs in 12.5% of births in the United States and can lead to risk of infant death or to lifelong serious health complications. A greater understanding by which the two main processes, uterine contraction and cervical remodeling are regulated is required to reduce rates of preterm birth. The cervix must undergo extensive remodeling through pregnancy in preparation for parturition, the process of labor and delivery of young. One key aspect of this dynamic process is a change in the composition and abundance of glycosaminoglycans (GAGs) and proteoglycans within the extracellular matrix, which influences the loss of tensile strength or stiffness of the cervix during labor. 23Na NMR spectroscopy has previously been validated as a method to quantify GAGs in tissues. In the current study, the Na+ concentration was measured at several time points through pregnancy in mouse cervices using 23Na NMR spectroscopy. The Na+ concentration increased progressively during pregnancy and peaked one day before birth followed by a rapid decline after birth. The same trend was seen in GAGs as measured by a biochemical assay using independent cervix samples over the course of pregnancy. We suggest that monitoring the Na+ concentration via 23Na NMR spectroscopy can serve as an informative physiological marker in evaluating the stages of cervical remodeling ex vivo and warrants further investigation to determine its utility as a diagnostic tool for the identification of women at risk for impending preterm birth.

Magnetic resonance imaging vs. transvaginal ultrasound for cervical length assessment in the second half of pregnancy

The purpose of this cross-sectional study involving 42 women between 20 and 39 weeks gestation was to compare transvaginal ultrasound (TVUS) vs. magnetic resonance imaging (MRI) in the assessment of cervical length measurement during the second half of pregnancy and to evaluate the reproducibility of cervical measurements obtained through MRI. Cervical length was measured through TVUS by a single examiner. On the same day, all women also had MRI and cervical length was assessed by two independent blinded observers. There were no significant differences in the mean cervical length obtained through TVUS and MRI (paired t-test, p = 0.191). The Bland-Altman test indicated concordance between measurements obtained through methods as well as good intra- and interobserver reproducibility for MRI measurements. Intraclass correlation coefficient was 0.990 (95% confidence interval [CI]: 0.982 to 0.995; p < 0.001) for measurements performed using MRI by two different observers and 0.995 (95% CI: 0.991 to 0.997; p < 0.001) for measurements performed using the same method by a single operator. Cervical length measured through TVUS and MRI does not differ significantly. There is a good reproducibility of cervical measurements obtained through MRI.