London, Mar 15 (IANS): MRI of the cervix is more accurate than ultrasound at predicting if some women will have a preterm birth, says a new study.

Early dilation of the cervix, a neck of tissue connecting the uterus with the vagina, during pregnancy can lead to premature delivery. Women in their second trimester of pregnancy with a cervix measuring 15 millimetres or less, as seen on ultrasound, are considered to be at higher risk of preterm birth.

However, ultrasound has limitations as a predictor of preterm birth, as it does not provide important information on changes in cervical tissue in the antepartum phase just before childbirth, the study pointed out.

"A better understanding of the process of antepartum cervical remodeling, loosely divided in two distinct phases called softening and ripening, is critical to improve the diagnosis of cervical malfunction and anticipate the occurrence of birth," said the study's lead author Gabriele Masselli from Sapienza University in Rome, Italy.

The study appeared in the online edition of the journal Radiology.

The researchers used an MRI technique called diffusion-weighted imaging (DWI) to examine pregnant women who had been referred for suspected fetal or placental abnormality.

Each of the 30 pregnant women in the study had a sonographically short cervix and a positive fetal fibronectin test between 23 and 28 weeks of gestation.

Fetal fibronectin is a glue-like protein that helps hold the fetal sac to the uterine lining, and the presence of it before week 35 of gestation may indicate a higher risk of preterm birth.

Of the 30 women, eight, or 27 percent, delivered within a week of the MRI examination.

The researchers found that local cell density of the inner, subglandular zone of the cervix measured high in MRI of patients with impending delivery.