title: Impact of Missing Data for Body Mass Index in an Epidemiologic Study.
abstract: Objective To assess the potential impact of missing data on body mass index (BMI) on the association between prepregnancy obesity and specific birth defects. Methods Data from the National Birth Defects Prevention Study (NBDPS) were analyzed. We assessed the factors associated with missing BMI data among mothers of infants without birth defects. Four analytic methods were then used to assess the impact of missing BMI data on the association between maternal prepregnancy obesity and three birth defects; spina bifida, gastroschisis, and cleft lip with/without cleft palate. The analytic methods were: (1) complete case analysis; (2) assignment of missing values to either obese or normal BMI; (3) multiple imputation; and (4) probabilistic sensitivity analysis. Logistic regression was used to estimate crude and adjusted odds ratios (aOR) and 95 % confidence intervals (CI). Results Of NBDPS control mothers 4.6 % were missing BMI data, and most of the missing values were attributable to missing height (~90 %). Missing BMI data was associated with birth outside of the US (aOR 8.6; 95 % CI 5.5, 13.4), interview in Spanish (aOR 2.4; 95 % CI 1.8, 3.2), Hispanic ethnicity (aOR 2.0; 95 % CI 1.2, 3.4), and <12 years education (aOR 2.3; 95 % CI 1.7, 3.1). Overall the results of the multiple imputation and probabilistic sensitivity analysis were similar to the complete case analysis. Conclusions Although in some scenarios missing BMI data can bias the magnitude of association, it does not appear likely to have impacted conclusions from a traditional complete case analysis of these data.
authors.affiliation: National Center for Chronic Disease Prevention and Health Pormotion, Centers for Disease Control and Prevention (CDC), Mail-Stop F76, 1600 Clifton Road, Atlanta, GA, 30333, USA. hir2@cdc.gov.
authors.forename: Hilda
authors.initials: H
authors.lastname: Razzaghi
authors.affiliation: National Center for Chronic Disease Prevention and Health Pormotion, Centers for Disease Control and Prevention (CDC), Mail-Stop F76, 1600 Clifton Road, Atlanta, GA, 30333, USA.
authors.forename: Sarah C
authors.initials: SC
authors.lastname: Tinker
authors.affiliation: Gillings School of Global Public Health and Carolina Population Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
authors.forename: Amy H
authors.initials: AH
authors.lastname: Herring
authors.affiliation: Rollins School of Public Health, Emory University, Atlanta, GA, USA.
authors.forename: Penelope P
authors.initials: PP
authors.lastname: Howards
authors.affiliation: UTHealth, School of Public Health, Houston, TX, USA.
authors.forename: D Kim
authors.initials: DK
authors.lastname: Waller
authors.affiliation: National Center for Chronic Disease Prevention and Health Pormotion, Centers for Disease Control and Prevention (CDC), Mail-Stop F76, 1600 Clifton Road, Atlanta, GA, 30333, USA.|Rollins School of Public Health, Emory University, Atlanta, GA, USA.|National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Cincinnati, OH, USA.
authors.forename: Candice Y
authors.initials: CY
authors.lastname: Johnson
mesh_terms: D000328:Adult; D015992:Body Mass Index; D000013:Congenital Abnormalities / Q000453:epidemiology* / Q000209:etiology; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D016015:Logistic Models; D009035:Mothers; D009765:Obesity / Q000453:epidemiology*; D016017:Odds Ratio; D011159:Population Surveillance; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology*; D012042:Registries; D016135:Spinal Dysraphism / Q000453:epidemiology*; D013851:Thinness / Q000150:complications / Q000453:epidemiology*; D014481:United States
keywords: BMI; Birth defect; Missing BMI; Missing data; NBDPS