Ultrasound is fine for flagging pregnant women who may be at risk of delivering their babies prematurely, but diffusion-weighted MRI can do better, accurately capturing subtle biomarkers of impending spontaneous delivery in asymptomatic women.

The Italian study behind the finding, which could help obstetricians know when to slow labor or better prepare NICU staffs for receiving new patients, posted online March 15 in Radiology.

Gabriele Masselli, MD, Sapienza University in Rome, and colleagues prospectively ordered pelvic 1.5-T MRI with diffusion weighting for 30 pregnant women whose sonograms showed a short cervix (15 mm or less) and who had a positive fetal fibronectin test between 23 and 28 weeks of gestation.

The latter result before week 35 generally points to a higher risk of preterm birth.

Of the 30 women, eight (27 percent) delivered within a week of the diffusion-weighted imaging (DWI), which shows differences in the mobility of water molecules in tissue.

The other 22 women delivered an average of 55 days later.

From the differences in water mobility, the researchers created apparent diffusion coefficient (ADC) maps, which quantify the density of local cells. They then compared differences in ADC values between the inner, subglandular zone of the cervix and the outer, stromal area.

The team found that, while stromal ADC and sonographic cervical length showed no difference between both groups, the subglandular ADC was higher in patients with impending delivery.

Masselli et al. describe how this elevation suggested cervical ripening, which is when the cervix rapidly changes in a way unique to the few days preceding the start of active labor.

In their study discussion, the authors state that theirs is the first test of DWI as a way to evaluate the uterine cervix in pregnant patients.

“In detail, the subglandular ADC was inversely correlated to the time interval between MRI and delivery,” they write, “and therefore emerged as a powerful imaging biomarker in evaluating patients with impending delivery.”

If this finding is confirmed in larger populations being studied for different risk factors, the authors add, “it could improve the policy of hospital admission and corticosteroid administration to improve fetal lung maturation. In addition, it could represent a new tool with which to monitor the efficacy of any drug putatively administered to slow the progression of impending labor.”