Diffusion-weighted MR of the Cervix Aids in Managing Preterm Labor
Diffusion-weighted MR (DWMR) imaging of the uterine cervix can predict impending preterm delivery in asymptomatic patients with premature shortening of the cervix, according to research presented at RSNA 2014.
The cervix is normally between 35 and 48 mm in length at 24 weeks gestation. A sonographic very short cervix (SCX) of less than 15 mm is a predictor of spontaneous preterm birth in late pregnancy.
“The clinical management of a sonographic short cervix in the mid-trimester of pregnancy is a major obstetrical challenge,” presenter Gabriele Masselli, M.D., explained. “Impending delivery is a severe condition that prompts admission to centers with neonatal intensive care units and an immediate administration of corticosteroids to induce fetal lung maturation. However, most patients with SCX will not deliver within one week.”
Daily Bulletin coverage of RSNA 2014 is available at RSNA.org/Bulletin
To better manage patients with symptoms of preterm labor, Dr. Masselli and a team of radiologists and gynecologists from Sapienza University of Rome investigated the use of MRI for cervical insufficiency. “To improve upon current methods of evaluating women for impending delivery, it is necessary to use parameters that are independent of cervical length and that reflect the process of fast cervical remodeling that occurs in the few days preceding labor,” he said.
The prospective study included 30 pregnant women (mean age 29) with a mean gestational age of 24 weeks who were diagnosed with SCX of less than 15 mm and positive fetal fibronectin (FN). The researchers performed sagittal diffusion-weighted imaging studies and created an apparent diffusion coefficient (ADC) map targeted to the subglandular area of the uterine cervix for each patient and calculated ADC subglandular, ADC stromal and ADC subglandular-ADC stromal values.
Eight of the 30 patients (the impending delivery group) ultimately delivered within seven days of admission to the hospital while 22 patients (late delivery group) delivered seven or more days after being hospitalized (mean of 32 days).
The ADC subglandular and ADC subglandular-ADC stromal values were significantly higher in patients within the impending delivery group than in the late delivery group. The ADCs of the cervical stroma did not help to differentiate the two groups.
Subglandular ADC Accurately Predicts Impending Delivery
The researchers’ statistical analysis showed that subglandular ADC was an extremely accurate parameter for predicting impending delivery with an overall sensitivity of 95 percent and a specificity of 95 percent.
“High ADC intensity of the subglandular area of the cervix accurately predicted impending delivery within seven days in patients presenting with a very short cervix,” Dr. Masselli said.
Dr. Masselli also noted that high intensity subglandular ADC values were poorly correlated to cervical length, suggesting that they result from mechanisms independent from those involved in cervical shortening. “When considering a diagnosis of impending preterm delivery, ADC maps targeted to the subglandular area of the uterine cervix greatly increase the positive predictive value of SCX and positive FN,” Dr. Masselli said.
Multicenter studies are needed to definitively assess the potential role of subglandular ADC as an imaging biomarker and to provide cost/benefit analyses, Dr. Masselli said. “We think the additional costs related to the MRI studies may be counterbalanced by a change in hospital admission policies for these patients who are typically hospitalized until delivery,” he said.