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Impact of Missing Data for Body Mass Index in an Epidemiologic Study


Razzaghi, Hilda; Tinker, Sarah C.; Herring, Amy H.; Howards, Penelope P.; Waller, D. Kim; Johnson, Candice Y.; & the National Birth Defects Prevention Study, (2016). Impact of Missing Data for Body Mass Index in an Epidemiologic Study. Maternal and Child Health Journal, 20(7), 1497-1505. PMCID: PMC4911272


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.


Reference Type

Journal Article

Year Published


Journal Title

Maternal and Child Health Journal


Razzaghi, Hilda
Tinker, Sarah C.
Herring, Amy H.
Howards, Penelope P.
Waller, D. Kim
Johnson, Candice Y.
the National Birth Defects Prevention Study,