title: Discrepancy in term calculation from second trimester ultrasound scan versus last menstrual period in women with type 1 diabetes.
abstract: OBJECTIVE
  To study differences in ultrasound-based compared to menstrual-based term estimation in women with type 1 diabetes.
  
  
  METHODS
  Nationwide register study.
  
  
  METHODS
  Norway.
  
  
  METHODS
  Deliveries in Norway 1999-2004 by women registered in the Norwegian Childhood Diabetes Registry (n = 342) and the background population (n = 307 248), with data on both ultrasound-based and menstrual-based gestational age notified in the Birth Registry of Norway. Births with major malformations were excluded.
  
  
  METHODS
  Linkage of two nationwide registries, the Medical Birth Registry of Norway and the Norwegian Childhood Diabetes Registry.
  
  
  METHODS
  Estimated gestational age at delivery based on routine second trimester ultrasound measurements and last menstrual period.
  
  
  RESULTS
  In women with type 1 diabetes, the distribution of gestational age at delivery was shifted considerably towards a lower gestational age when using second trimester ultrasound data for estimation, compared with last menstrual period data. The difference between the two estimation methods was larger among women with type 1 diabetes, although also evident in the general population. One in four women with diabetes and a certain last menstrual period date had their ultrasound-calculated term postponed 1 week or more, while one in 10 had it postponed 2 weeks or more. Corresponding numbers in the background population were one in five and one in 20.
  
  
  CONCLUSIONS
  We found a systematic postponement of ultrasound-based compared with menstrual-based term estimation in women with type 1 diabetes. Relying solely on routine ultrasound-based term calculation for delivery decision may imply a risk of going beyond an optimal pregnancy length.
authors.affiliation: Department of Pediatric Medicine, Oslo University Hospital, Oslo, Norway; Division of Epidemiology, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Ingvild
authors.initials: I
authors.lastname: Eidem
authors.forename: Siri
authors.initials: S
authors.lastname: Vangen
authors.forename: Tore
authors.initials: T
authors.lastname: Henriksen
authors.forename: Stein E
authors.initials: SE
authors.lastname: Vollset
authors.forename: Kristian F
authors.initials: KF
authors.lastname: Hanssen
authors.forename: Geir
authors.initials: G
authors.lastname: Joner
authors.forename: Lars C
authors.initials: LC
authors.lastname: Stene
mesh_terms: D000328:Adult; D003922:Diabetes Mellitus, Type 1 / Q000000981:diagnostic imaging*; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008598:Menstruation; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011254:Pregnancy in Diabetics / Q000000981:diagnostic imaging*; D012042:Registries; D047929:Term Birth; D016216:Ultrasonography, Prenatal
keywords: Type 1 diabetes; gestational length; last menstrual period; pregnancy; ultrasound