title: Preterm or not--an evaluation of estimates of gestational age in a cohort of women from Rural Papua New Guinea.
abstract: BACKGROUND
  Knowledge of accurate gestational age is required for comprehensive pregnancy care and is an essential component of research evaluating causes of preterm birth. In industrialised countries gestational age is determined with the help of fetal biometry in early pregnancy. Lack of ultrasound and late presentation to antenatal clinic limits this practice in low-resource settings. Instead, clinical estimators of gestational age are used, but their accuracy remains a matter of debate.
  
  
  METHODS
  In a cohort of 688 singleton pregnancies from rural Papua New Guinea, delivery gestational age was calculated from Ballard score, last menstrual period, symphysis-pubis fundal height at first visit and quickening as well as mid- and late pregnancy fetal biometry. Published models using sequential fundal height measurements and corrected last menstrual period to estimate gestational age were also tested. Novel linear models that combined clinical measurements for gestational age estimation were developed. Predictions were compared with the reference early pregnancy ultrasound (<25 gestational weeks) using correlation, regression and Bland-Altman analyses and ranked for their capability to predict preterm birth using the harmonic mean of recall and precision (F-measure).
  
  
  RESULTS
  Average bias between reference ultrasound and clinical methods ranged from 0-11 days (95% confidence levels: 14-42 days). Preterm birth was best predicted by mid-pregnancy ultrasound (F-measure: 0.72), and neuromuscular Ballard score provided the least reliable preterm birth prediction (F-measure: 0.17). The best clinical methods to predict gestational age and preterm birth were last menstrual period and fundal height (F-measures 0.35). A linear model combining both measures improved prediction of preterm birth (F-measure: 0.58).
  
  
  CONCLUSIONS
  Estimation of gestational age without ultrasound is prone to significant error. In the absence of ultrasound facilities, last menstrual period and fundal height are among the more reliable clinical measures. This study underlines the importance of strengthening ultrasound facilities and developing novel ways to estimate gestational age.
authors.affiliation: Walter and Eliza Hall Institute of Medical Research (WEHI), Melbourne, Australia; Department of Medical Biology, The University of Melbourne, Melbourne, Australia.
authors.forename: Stephan
authors.initials: S
authors.lastname: Karl
authors.affiliation: Walter and Eliza Hall Institute of Medical Research (WEHI), Melbourne, Australia; Department of Medical Biology, The University of Melbourne, Melbourne, Australia.
authors.forename: Connie S N
authors.initials: CS
authors.lastname: Li Wai Suen
authors.affiliation: Department of Medicine (Royal Melbourne Hospital), The University of Melbourne, Melbourne, Australia; Papua New Guinea Institute of Medical Research (PNG IMR), Goroka, Papua New Guinea.
authors.forename: Holger W
authors.initials: HW
authors.lastname: Unger
authors.affiliation: Papua New Guinea Institute of Medical Research (PNG IMR), Goroka, Papua New Guinea.
authors.forename: Maria
authors.initials: M
authors.lastname: Ome-Kaius
authors.affiliation: Department of Obstetrics and Gynaecology, University of Papua New Guinea, Port Moresby, Papua New Guinea.
authors.forename: Glen
authors.initials: G
authors.lastname: Mola
authors.affiliation: Centre for Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, United Kingdom; Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
authors.forename: Lisa
authors.initials: L
authors.lastname: White
authors.affiliation: Papua New Guinea Institute of Medical Research (PNG IMR), Goroka, Papua New Guinea.
authors.forename: Regina A
authors.initials: RA
authors.lastname: Wangnapi
authors.affiliation: Department of Medicine (Royal Melbourne Hospital), The University of Melbourne, Melbourne, Australia.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Rogerson
authors.affiliation: Walter and Eliza Hall Institute of Medical Research (WEHI), Melbourne, Australia; Department of Medical Biology, The University of Melbourne, Melbourne, Australia; Barcelona Institute for Global Health (ISGlobal), Barcelona, Spain.
authors.forename: Ivo
authors.initials: I
authors.lastname: Mueller
mesh_terms: D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D008875:Middle Aged; D015233:Models, Statistical; D010219:Papua New Guinea; D011247:Pregnancy; D047928:Premature Birth / Q000175:diagnosis / Q000453:epidemiology*; D012424:Rural Population / Q000706:statistics & numerical data*