title: Normal range of maternal serum vitamin d at 11-13 weeks' gestation.
abstract: OBJECTIVE
  To establish a normal range of maternal serum levels of total vitamin D at 11-13 weeks' gestation and examine factors from maternal characteristics and obstetric history affecting these levels.
  
  
  METHODS
  Serum 25-hydroxyvitamin D [25(OH)D] was measured by liquid chromatography-tandem mass spectrometry in 1,000 singleton pregnancies with normal outcome. Multiple regression analysis was used to determine the factors from maternal characteristics and obstetric history affecting the measured 25(OH)D levels and the regression model was used to convert each measurement into a multiple of the median (MoM).
  
  
  RESULTS
  Serum 25(OH)D increased with maternal age, decreased with body mass index (BMI), it was higher in the summer than other months and when conception was assisted than spontaneous and it was lower in cigarette smokers and in women of African and Asian racial origin compared to Caucasians. In Caucasian, non-smoking women, with BMI below 25, conceiving spontaneously and sampled in the summer months the estimated 5th, 10th, 50th, 90th and 95th percentiles of 25(OH)D were 10.8, 14.7, 30.7, 48.2 and 55.7 ng/ml, respectively.
  
  
  CONCLUSIONS
  Maternal serum 25(OH)D concentration at 11-13 weeks is affected by season of blood sampling and maternal characteristics.
authors.affiliation: Harris Birthright Research Centre for Fetal Medicine, King's College Hospital, London, UK.
authors.forename: Christina K H
authors.initials: CK
authors.lastname: Yu
authors.forename: Rebecca
authors.initials: R
authors.lastname: Ertl
authors.forename: Robert
authors.initials: R
authors.lastname: Samaha
authors.forename: Ranjit
authors.initials: R
authors.lastname: Akolekar
authors.forename: Kypros H
authors.initials: KH
authors.lastname: Nicolaides
mesh_terms: D000328:Adult; D002853:Chromatography, Liquid; D005260:Female; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy / Q000097:blood*; D011261:Pregnancy Trimester, First; D011446:Prospective Studies; D012044:Regression Analysis; D012621:Seasons; D053719:Tandem Mass Spectrometry; D014807:Vitamin D / Q000097:blood*
chemical_list: D014807:Vitamin D