Common tests for preterm birth not useful for routine screening of first-time pregnancies

Two methods thought to hold promise in predicting preterm delivery in first-time pregnancies identified only a small proportion of cases and do not appear suitable for widespread screening, according to a large study by a National Institutes of Health research network.

The study focused on spontaneous preterm delivery—labor that occurs naturally—rather than delivery initiated for medical need, such as cesarean surgery or induced labor.

The study authors evaluated routine ultrasound examination of the uterine cervix, the lower part of the uterus that shortens and opens during labor. Previous studies have indicated that a short cervix early in pregnancy could be a warning sign of impending preterm birth. The researchers also evaluated testing for fetal fibronectin, a glue-like protein that secures the amniotic sac to the inside of the uterus. Some studies have suggested that the presence of fetal fibronectin in the vagina early in pregnancy could signal early labor.

Normal length and short cervix.
Image Credit: Courtesy of the National Institutes of Health

However, after screening more than 9,000 women throughout pregnancy, each test identified only a small proportion of the women who would eventually deliver preterm.

“These methods of assessing women in their first pregnancy do not identify most of those who will later go on to have a spontaneous preterm delivery,” said the study’s senior author, Uma Reddy, M.D., of the Pregnancy and Perinatology Branch at NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development. “There is a need to develop better screening tests that can be performed early in pregnancy.”

The article appears in the Journal of the American Medical Association.

The study included 9,410 women pregnant with a single fetus at eight research centers in the United States. It was conducted as part of the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be (nuMoM2b), which aims to improve the care of women during their first pregnancy and to find new ways to identify impending preterm birth and other adverse pregnancy conditions.

The women underwent ultrasound testing to measure cervical length at 16 to 22 weeks of pregnancy and again from 22 to 31 weeks of pregnancy. Fetal fibronectin tests were conducted at 6 to 14 weeks, 16 to 22 weeks and 22 to 30 weeks. A short cervix was defined as less than 25 mm.

Of the women tested at 16 to 22 weeks, 35 of 439 women (8 percent) who delivered spontaneously before the 37th week of pregnancy had a short cervix. At 22 to 31 weeks, 94 of 403 women (23.3 percent) who delivered prematurely had a short cervix.

For the fibronectin test at 16 to 22 weeks, 30 of 410 women (7.3 percent) who delivered spontaneously before the 37th week had high fibronectin levels. At 22 to 30 weeks, 31 of 384 women (8.1 percent) who delivered prematurely had high fibronectin levels. The authors defined a high fibronectin level as 50 ng/mL or greater.

The researchers found no benefit to combining the results of the two tests. They concluded that, alone and together, the methods did not identify enough preterm births to support routine screening of first-time pregnancies.

REFERENCE: Esplin, MS, et al. Predictive accuracy of serial transvaginal cervical length by ultrasound and quantitative vaginal fetal fibronectin for spontaneous preterm birth among nulliparous women. JAMA. 2017:317(10)1-10. Doi:10.1001/jama.2017.1373.

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About the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD): NICHD conducts and supports research in the United States and throughout the world on fetal, infant and child development; maternal, child and family health; reproductive biology and population issues; and medical rehabilitation. For more information, visit NICHD’s website.

About the National Institutes of Health (NIH): NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit http://www.nih.gov.