Can shortened midtrimester cervical length predict very early spontaneous preterm birth? John Owen, MD, a Nicole Yost, MD, b Vincenzo Berghella, MD, c Cora MacPherson, PhD, d Melissa Swain, RN, e Gary A. Dildy III, MD, f Menachem Miodovnik, MD, g Oded Langer, MD, h Baha Sibai, MD, i for the Maternal-Fetal Medicine Units Network, Bethesda, Md University of Alabama at Birmingham a ; University of Texas Southwestern Medical Center, Dallas b ; Thomas Jefferson University, Philadelphia, Pa c ; George Washington University Biostatistics Center, Bethesda, Md d ; Wake Forest University, Winston-Salem, NC e ; University of Utah, Salt Lake City f ; University of Cincinnati g ; University of Texas at San Antonio h ; University of Tennessee, Memphis i Received for publication July 18, 2003; revised November 11, 2003; accepted November 18, 2003 – Objective: The study was undertaken to test the hypothesis that shortened midtrimester cervical length is more predictive of early (!26 weeks) than later (26-34 weeks) spontaneous preterm birth. Study design: This is a secondary analysis of a blinded, multicenter observational study of 183 women with a prior preterm birth. Vaginal sonography was begun at 16 to18 weeks’ gestation and scheduled every 2 weeks (maximum 4 scans per patient). Cervical length and any observed dynamic shortening were recorded at each visit to determine the shortest observed cervical length from 16 to 24 weeks’ gestation. The shortest cervical length measurements were categorized as less than 25 mm, 25 to 29 mm and 30 mm or greater. The initial cervical length was also compared with the shortest cervical length to categorize patients on the basis of the timing of cervical short- ening 30 mm or less. Contingency table, linear regression, and survival analysis were used to an- alyze the relationship between cervical length groups and spontaneous preterm birth. Results: In both the less than 25 mm and 25 to 29 mm groups, the incidence of spontaneous mid- trimester birth (!26 weeks) was higher than the incidence of later (26-34 weeks) preterm birth (!25 mm group: 37% vs 19%; 25-29 mm group: 16% vs 3%, respectively) as compared with women with a shortest cervical length 30 mm or greater, who had rates of 1% and 9% respec- tively (P!.0001). Similarly, women who had an initial cervical length 30 mm or less and those who shortened their cervix to 30 mm or less before 22 weeks were also more likely to experience a midtrimester than later preterm birth, whereas women who shortened their cervix 30 mm or less KEY WORDS Cervical length Vaginal sonography Preterm birth Midtrimester birth Presented at the 2002 Annual Meeting of the Society for Gynecologic Investigation in Los Angeles, Calif, March 21, 2002. Supported by the following grants from the National Institute of Child Health And Human Development: HD27869, HD21414, HD27860, HD27905, HD36801, HD34116, HD34210, HD34208, HD34136 Reprints not available from the authors. E-mail: johnowen@uab.edu American Journal of Obstetrics and Gynecology (2004) 191, 298e303 www.elsevier.com/locate/ajog 0002-9378/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.ajog.2003.11.025