Among first-time pregnant women, quantitative vaginal fetal fibronectin and serial transvaginal ultrasound cervical length had low predictive accuracy for spontaneous preterm birth, according to a study published by JAMA.
M. Sean Esplin, MD, from Intermountain Healthcare in Murray, Utah, and colleagues conducted a prospective observational cohort study of nulliparous women with singleton pregnancies from 8 clinical states across the United States from October 2010 to May 2014. Pregnant women who planned to deliver their infants at one of the clinical site hospitals were recruited before 14 weeks gestational age. Transvaginal cervical length and quantitative vaginal fetal fibronectin levels were reviewed at 2 study visits 4 or more weeks apart. Women and clinicians were blinded to results unless cervical shortening less than 15 mm was identified.
The primary outcome was spontaneous preterm birth at less than 37 weeks of gestation. Cervical length and quantitative fetal fibronectin were considered independently and together at each visit. Measurement distributions were compared for spontaneous preterm birth vs all other births. The secondary outcome was spontaneous preterm birth before 32 weeks of gestation.
The study included 9410 women with a median age of 27 years; 60.7% non-Hispanic white, 13.8% non-Hispanic black, 16.5% Hispanic, 4.0% Asian, and 5.1% other. Of these women, 474 (5.0%) had spontaneous preterm births, 335 (3.6%) had medically indicated preterm births, and 8601 (91.4%) had term births. Among the women with spontaneous preterm births, cervical length of 25 mm or less occurred in 35 of 439 (8.0%) at 16 to 22 weeks’ gestation and in 94 of 403 (23.3%) at 22 to 30 weeks’ gestation. Fetal fibronectin levels of 50 ng/mL or greater at 16 to 22 weeks identified 30 of 410 women (7.3%) with spontaneous preterm birth and 31 of 384 (8.1%) at 22 to 30 weeks.
“Among nulliparous women with singleton pregnancies, quantitative vaginal fetal fibronectin and serial transvaginal ultrasound cervical length had low predictive accuracy for spontaneous preterm birth,” said the authors. “These findings do not support routine use of these tests in such women.”
- Esplin MS, Elovitz MA, Iams JD, et al. Predictive accuracy of serial transvaginal cervical lengths and quantitative vaginal fetal fibronectin levels for spontaneous preterm birth among nulliparous women. JAMA. 14 March 2017. doi:10.1001/jama.2017.1373