title: Prospective population-based cohort study of maternal obesity as a source of error in gestational age estimation at 11-14 weeks.
abstract: BACKGROUND
  An impact of maternal obesity on ultrasound dating of pregnancy at 11-14 gestational weeks is possible and was investigated.
  
  
  METHODS
  A prospective cohort study based on the Danish national population during a 4-year period in which we entered all mothers with singleton pregnancies who had a known last menstrual period (LMP), a recorded booking of body mass index (BMI), and a late first trimester ultrasound dating scan using crown-rump-length measurement (gestational age 11+0-13+6weeks). Almost all scans were performed transabdominally. Transvaginal ultrasound was only performed in the case of limited visibility by transabdominal scanning. Differences between LMP and ultrasound estimated date of delivery (EDD) were stratified by BMI classes. Odds ratios (ORs) were calculated and adjusted for maternal age, parity and smoking.
  
  
  RESULTS
  In total, 187 486 women were analyzed: 21.8% were overweight and 12.3% obese. Ultrasound EDD was ≥7 days later than by LMP in 5.8% of normal-weight women, 7.3% of obese women, and 10.0% of women with morbid obesity. Compared with normal BMI (18.5-24.9), the OR for postponing EDD increased with increasing BMI; BMI 25-29.9 [OR 0.97, 95% confidence interval (CI) 0.93-1.02], BMI 30-34.9 (OR 1.14, 95% CI 1.07-1.23), BMI 35-39.9 (OR 1.28, 95% CI 1.15-1.42), and BMI 40+ (OR 1.73, 95% CI 1.50-1.98). Lean pregnant women (BMI <18.5) also had a higher chance of having EDD postponed 7 days or more (OR 1.11, 95% CI 1.01-1.22).
  
  
  CONCLUSIONS
  Rising maternal BMI appears to be associated with postponement of ultrasound EDD.
authors: Fetal Medicine Unit, Department of Obstetrics and Gynecology, Odense University Hospital, Odense, Denmark. geske.bak@rsyd.dk.
authors: Geske S
authors: GS
authors: Bak
authors: Fetal Medicine Unit, Department of Obstetrics and Gynecology, Odense University Hospital, Odense, Denmark.
authors: Lene
authors: L
authors: Sperling
authors: Center of Reproduction Epidemiology, Institute of Clinical Sciences, Lund University, Lund, Sweden.
authors: Karin
authors: http://orcid.org/0000-0001-5765-2630
authors: K
authors: Källén
authors: National Center for Fetal Medicine, Trondheim University Hospital, Trondheim, Norway.|Department of Laboratory Medicine, Children's and Women's Health, Norwegian University of Science and Technology, Trondheim, Norway.
authors: Kjell Å
authors: http://orcid.org/0000-0002-1788-4063
authors: KÅ
authors: Salvesen
mesh_terms: D000328:Adult; D015992:Body Mass Index; D015331:Cohort Studies; D018568:Crown-Rump Length; D016208:Databases, Factual; D003718:Denmark; D005260:Female; D005865:Gestational Age; D006801:Humans; D009765:Obesity; D016017:Odds Ratio; D011247:Pregnancy; D011248:Pregnancy Complications; D011261:Pregnancy Trimester, First; D016216:Ultrasonography, Prenatal
keywords: Overweight; body mass index; estimated date of delivery; first trimester screening; last menstrual period; obesity; pregnancy dating; ultrasound