title: Association between second-trimester cervical length and spontaneous preterm birth in twin pregnancies.
abstract: OBJECTIVE
  The purpose of this study was to define normal second-trimester cervical length (CL) measurements and to estimate the association between second-trimester CL and spontaneous preterm birth (SPTB) in twin pregnancies.
  
  
  METHODS
  A retrospective cohort of 309 asymptomatic patients with twin pregnancies who had routine outpatient CL assessment in the second trimester was studied. We looked at the gestational age periods of 16 to 17 6/7, 18 to 19 6/7, 20 to 21 6/7, and 22 to 23 6/7 weeks. We estimated the association between the CL measurement during each period and SPTB. A short CL was defined both as a CL at or below the 10th percentile for gestational age and 25 mm or less. We also performed regression analyses controlling for a number of clinically important factors: maternal age, chorionicity, in vitro fertilization, multifetal reduction, prior term births, prior preterm births, prepregnancy body mass index, and cerclage.
  
  
  RESULTS
  The CL measurement at 16 to 17 6/7 weeks was not associated with gestational age at delivery or SPTB. At 18 to 19 6/7 and 20 to 21 6/7 weeks, the CL measurement was not significantly associated with gestational age at delivery or SPTB before 28 and 32 weeks. There was an association with SPTB before 35 weeks. At 22 to 23 6/7 weeks, the CL measurement had a significant association with gestational age at delivery and SPTB before 28, 32, and 35 weeks (P < .05). A short CL at 22 to 23 6/7 weeks was significantly associated with SPTB before 32 and 35 weeks (P < .05).
  
  
  CONCLUSIONS
  In second-trimester twin pregnancies, the strongest association between CL and SPTB is at 22 to 23 6/7 weeks.
authors.affiliation: Department of Obstetrics, Gynecology, and Reproductive Science, Mount Sinai School of Medicine, New York, New York, USA. nfox@mfmnyc.com
authors.forename: Nathan S
authors.initials: NS
authors.lastname: Fox
authors.forename: Andrei
authors.initials: A
authors.lastname: Rebarber
authors.forename: Ashley S
authors.initials: AS
authors.lastname: Roman
authors.forename: Chad K
authors.initials: CK
authors.lastname: Klauser
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Saltzman
mesh_terms: D000328:Adult; D023802:Cerclage, Cervical; D002584:Cervix Uteri / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D005260:Female; D005865:Gestational Age; D006801:Humans; D016015:Logistic Models; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011272:Pregnancy, Multiple; D047928:Premature Birth / Q000000981:diagnostic imaging* / Q000517:prevention & control; D012189:Retrospective Studies; D016216:Ultrasonography, Prenatal