Historically, clinicians have relied on medical risk factors and clinical symptoms for preterm birth risk assessment. In nulliparous women, clinicians may rely solely on reported symptoms to assess for the risk of preterm birth. The routine use of ultrasound during pregnancy offers the opportunity to incorporate quantitative ultrasound scanning of the cervix to potentially improve assessment of preterm birth risk.
This study aimed to investigate the efficiency of quantitative ultrasound measurements at relatively early stages of pregnancy to enhance identification of women who might be at risk for spontaneous preterm birth.
A prospective cohort study of pregnant women was conducted with volunteer participants receiving care from the University of Illinois Hospital in Chicago, Illinois. Participants received a standard clinical screening followed by 2 research screenings conducted at 20±2 and 24±2 weeks. Quantitative ultrasound scans were performed during research screenings by registered diagnostic medical sonographers using a standard cervical length approach. Quantitative ultrasound features were computed from calibrated raw radiofrequency backscattered signals. Full-term birth outcomes and spontaneous preterm birth outcomes were included in the analysis. Medically indicated preterm births were excluded from the analysis. Using data from each visit, logistic regression with Akaike information criterion feature selection was conducted to derive predictive models for each time frame based on historical clinical and quantitative ultrasound features. Model evaluations included a likelihood ratio test of quantitative ultrasound features, cross-validated receiver operating characteristic curve analysis, sensitivity, and specificity.
On the basis of historical clinical features alone, the best predictive model had an estimated receiver operating characteristic area under the curve of 0.56±0.03. By the time frame of Visit 1, a predictive model using both historical clinical and quantitative ultrasound features provided a modest improvement in the area under the curve (0.63±0.03) relative to that of the predictive model using only historical clinical features. By the time frame of Visit 2, the predictive model using historical clinical and quantitative ultrasound features provided significant improvement (likelihood ratio test, P<.01), with an area under the curve of 0.69±0.03.
Accurate identification of women at risk for spontaneous preterm birth solely through historical clinical features has been proven to be difficult. In this study, a history of preterm birth was the most significant historical clinical predictor of preterm birth risk, but the historical clinical predictive model performance was not statistically significantly better than the no-skill level. According to our study results, including quantitative ultrasound yields a statistically significant improvement in risk prediction as the pregnancy progresses.

Cervical remodeling is an important aspect of birth timing. Before cervical ripening, the collagen fibers are arranged in a closely interweaved network, but during ripening, the fibers become disorganized and the cervix becomes more hydrated. To quantitatively measure cervical remodeling, we need a noninvasive method to monitor changes in cervical collagen fiber organization and hydration in vivo.
To use diffusion tensor imaging to image and quantify the spatial and temporal differences in cervical microstructure between normal early and late pregnancies.
After institutional review board approval and consent, a group of healthy women in early pregnancy (22 patients at 12-14 weeks\' gestation) and a group in late pregnancy (27 patients at 36-38 weeks\' gestation) underwent magnetic resonance imaging on a Siemens MAGNETOM Vida 3 Tesla unit. Diffusion tensor imaging of the cervix in the axial plane was performed with a two-dimensional single-shot echo planar imaging diffusion-weighted sequence. In early and late pregnancy groups, the differences of the diffusion tensor imaging measures were compared between the subglandular zone and the outer stroma regions of the cervix. In addition, the diffusion tensor imaging measures were compared between the early and late pregnancy groups. Finally, for the late pregnancy group, the diffusion tensor imaging measures were compared between the primipara and multipara groups.
Diffusion tensor imaging measures of microstructure significantly differed between the subglandular zone and outer stroma regions of the cervix in both early and late pregnancies. In the subglandular zone, fractional anisotropy was lower in the late pregnancy group than in the early pregnancy group (0.37 [0.34-0.42] vs 0.50 [0.43-0.58]; P<.0005), suggesting increased collagen fiber disorganization in this zone. In addition, mean diffusivity was higher in the late pregnancy group than in the early pregnancy group (1.84 [1.73-2.02] mm2/sec×10-3 vs 1.56 [1.42-1.69] mm2/sec×10-3; P=.001), suggesting increased hydration in the subglandular zone. In the outer stroma, neither fractional anisotropy (0.44 [0.40-0.50] vs 0.41 [0.37-0.43]; P=.095) nor mean diffusivity (2.09 [1.92-2.25] mm2/sec×10-3 vs 2.12 [2.04-2.24] mm2/sec×10-3; P=.269) significantly differed between early pregnancy and late pregnancy, suggesting insignificant temporal microstructural changes in this cervical zone. Diffusion tensor imaging measures did not significantly differ between cervixes from primiparous and multiparous women in late pregnancy.
This in vivo study demonstrates that diffusion tensor imaging can noninvasively quantify the microstructural differences in collagen fiber organization and hydration in cervical subregions between early pregnancy and late pregnancy.

The process of parturition is poorly understood, but the cervix clearly plays a key role. Because of this, recent research efforts have been directed at objective quantification of cervical remodeling. Investigation has focused on two basic areas: (1) quantification of tissue deformability and (2) presence, orientation, and/or concentration of microstructural components (e.g. collagen). Methods to quantify tissue deformability include strain elastography and shear wave elasticity imaging (SWEI). Methods to describe tissue microstructure include attenuation and backscatter. A single parameter is unlikely to describe the complexities of cervical remodeling, but combining related parameters should improve accuracy of cervical evaluation. This chapter reviews options for cervical tissue characterization.