title: The capacity of mid-pregnancy cervical length to predict preterm birth in low-risk women: a national cohort study.
abstract: BACKGROUND
  We investigated the predictive capacity of mid-trimester cervical length (CL) measurement for spontaneous and iatrogenic preterm birth.
  
  
  METHODS
  We performed a prospective observational cohort study in nulliparous women and low-risk multiparous women with a singleton pregnancy between 16(+0) and 21(+6) weeks of gestation. We assessed the prognostic capacity of transvaginally measured mid-trimester CL for spontaneous and iatrogenic preterm birth (<37 weeks) using likelihood ratios (LR) and receiver-operating-characteristic analysis. We calculated numbers needed to screen to prevent one preterm birth assuming different treatment effects. Main outcome measures were preterm birth <32, <34 and <37 weeks.
  
  
  RESULTS
  We studied 11,943 women, of whom 666 (5.6%) delivered preterm: 464 (3.9%) spontaneous and 202 (1.7%) iatrogenic. Mean CL was 44.1 mm (SD 7.8 mm). In nulliparous women, the LRs for spontaneous preterm birth varied between 27 (95% CI 7.7-95) for a CL ≤ 20 mm, and 2.0 (95% CI 1.6-2.5) for a CL between 30 and 35 mm. For low-risk multiparous women, these LRs were 37 (95% CI 7.5-182) and 1.5 (95% CI 0.97-2.2), respectively. Using a cut-off for CL ≤ 30 mm, 28 (6.0%) of 464 women with spontaneous preterm birth were identified. The number needed to screen to prevent one case of preterm birth was 618 in nulliparous women and 1417 for low-risk multiparous women (40% treatment effect, cut-off 30 mm).
  
  
  CONCLUSIONS
  In women at low risk of preterm birth, CL predicts spontaneous preterm birth. However, its isolated use as a screening tool has limited value due to low sensitivity.
authors.affiliation: Department of Obstetrics and Gynecology, Academic Medical Center, Amsterdam, the Netherlands.
authors.forename: Jeanine
authors.initials: J
authors.lastname: van der Ven
authors.affiliation: Department of Obstetrics and Gynecology, VU University Medical Center, Amsterdam, the Netherlands.
authors.forename: Melanie A
authors.initials: MA
authors.lastname: van Os
authors.affiliation: Department of Obstetrics and Gynecology, Academic Medical Center, Amsterdam, the Netherlands.
authors.forename: Brenda M
authors.initials: BM
authors.lastname: Kazemier
authors.affiliation: Department of Obstetrics and Gynecology, Academic Medical Center, Amsterdam, the Netherlands.
authors.forename: Emily
authors.initials: E
authors.lastname: Kleinrouweler
authors.affiliation: Department of Obstetrics and Gynecology, Máxima Medical Center, Veldhoven, the Netherlands.|Department of Midwifery Science, AVAG/EMGO Institute for Health and Care Research, VU University Medical Center, Amsterdam, the Netherlands.
authors.forename: Corine J
authors.initials: CJ
authors.lastname: Verhoeven
authors.affiliation: Department of Obstetrics and Gynecology, Academic Medical Center, Amsterdam, the Netherlands.
authors.forename: Esteriek
authors.initials: E
authors.lastname: de Miranda
authors.affiliation: Department of Neonatology, Emma Children's Hospital Academic Medical Center, Amsterdam, the Netherlands.
authors.forename: Aleid G
authors.initials: AG
authors.lastname: van Wassenaer-Leemhuis
authors.affiliation: Obstetrics and Prenatal Center FARA, Ede, the Netherlands.
authors.forename: Petra N
authors.initials: PN
authors.lastname: Kuiper
authors.affiliation: Department of Obstetrics and Gynecology, Máxima Medical Center, Veldhoven, the Netherlands.
authors.forename: Martina
authors.initials: M
authors.lastname: Porath
authors.affiliation: Department of Obstetrics and Gynecology, Maastricht University Medical Center, Maastricht, the Netherlands.
authors.forename: Christine
authors.initials: C
authors.lastname: Willekes
authors.affiliation: Department of Obstetrics and Gynecology, Radboud University Nijmegen, Nijmegen, the Netherlands.
authors.forename: Mallory D
authors.initials: MD
authors.lastname: Woiski
authors.affiliation: Ziekenhuisgroep Twente Hospital, Almelo, the Netherlands.
authors.forename: Marko J
authors.initials: MJ
authors.lastname: Sikkema
authors.affiliation: Department of Obstetrics and Gynecology, Atrium Medical Center, Heerlen, the Netherlands.
authors.forename: Frans J M E
authors.initials: FJ
authors.lastname: Roumen
authors.affiliation: Department of Clinical Epidemiology, Biostatistics and Bioinformatics (KEBB), Academic Medical Center, Amsterdam, the Netherlands.
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Bossuyt
authors.affiliation: Department of Obstetrics and Gynecology, Leiden University Medical Center, Leiden, the Netherlands.
authors.forename: Monique C
authors.initials: MC
authors.lastname: Haak
authors.affiliation: Department of Obstetrics and Gynecology, VU University Medical Center, Amsterdam, the Netherlands.
authors.forename: Christianne J M
authors.initials: CJ
authors.lastname: de Groot
authors.affiliation: The Robinson Institute, School of Paediatrics and Reproductive Health, University of Adelaide, Adelaide, South Australia, Australia.
authors.forename: Ben W J
authors.initials: BW
authors.lastname: Mol
authors.affiliation: Department of Obstetrics and Gynecology, Academic Medical Center, Amsterdam, the Netherlands.
authors.forename: Eva
authors.initials: E
authors.lastname: Pajkrt
mesh_terms: D000328:Adult; D054791:Cervical Length Measurement; D002584:Cervix Uteri / Q000000981:diagnostic imaging*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D016013:Likelihood Functions; D009426:Netherlands / Q000453:epidemiology; D009929:Organ Size; D010298:Parity; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D047928:Premature Birth / Q000175:diagnosis* / Q000453:epidemiology*; D011379:Prognosis; D012372:ROC Curve
keywords: Cervical length measurement; low-risk population; preterm birth