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Bias in Self-reported Prepregnancy Weight Across Maternal and Clinical Characteristics

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Abstract

Objectives

Prepregnancy body mass index (BMI) and gestational weight gain (GWG) are known determinants of maternal and child health; calculating both requires an accurate measure of prepregnancy weight. We compared self-reported prepregnancy weight to measured weights to assess reporting bias by maternal and clinical characteristics.

Methods

We conducted a retrospective cohort study among pregnant women using electronic health records (EHR) data from Kaiser Permanente Northwest, a non-profit integrated health care system in Oregon and southwest Washington State. We identified women age ≥ 18 years who were pregnant between 2000 and 2010 with self-reported prepregnancy weight, ≥ 2 measured weights between ≤ 365-days-prior-to and ≤ 42-days-after conception, and measured height in their EHR. We compared absolute and relative difference between self-reported weight and two “gold-standards”: (1) weight measured closest to conception, and (2) usual weight (mean of weights measured 6-months-prior-to and ≤ 42-days-after conception). Generalized-estimating equations were used to assess predictors of misreport controlling for covariates, which were obtained from the EHR or linkage to birth certificate.

Results

Among the 16,227 included pregnancies, close agreement (± 1 kg or ≤ 2%) between self-reported and closest-measured weight was 44% and 59%, respectively. Overall, self-reported weight averaged 1.3 kg (SD 3.8) less than measured weight. Underreporting was higher among women with elevated BMI category, late prenatal care entry, and pregnancy outcome other than live/stillbirth (p < .05). Using self-reported weight, BMI was correctly classified for 91% of pregnancies, but ranged from 70 to 98% among those with underweight or obesity, respectively. Results were similar using usual weight as gold standard.

Conclusions for Practice

Accurate measure of prepregnancy weight is essential for clinical guidance and surveillance efforts that monitor maternal health and evaluate public-health programs. Identification of characteristics associated with misreport of self-reported weight can inform understanding of bias when assessing the influence of prepregnancy BMI or GWG on health outcomes.

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Data Availability

The study protocol is available upon request.

Code Availability

The statistical analysis programming code is available upon request.

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Funding

Research reported in this publication was funded by Contract # CDC 200-2016-M-91914, “Assessment of Self-Reported Weight,” from the Centers for Disease Control and Prevention (awarded to Dr. Bulkley).

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Contributions

All authors contributed to the intellectual content of this paper and have met the following 3 requirements: (a) significant contributions to the conception and design, acquisition of data, or analysis and interpretation of data; (b) drafting or revising the article for intellectual content; and (c) final approval of the published article.

Corresponding author

Correspondence to Andrea J. Sharma.

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Conflict of interest

All authors declare that they have no conflict of interest.

Disclaimer

The findings and conclusions in this article are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention or Kaiser Permanente.

Ethical Approval

All procedures performed in this study were in accordance with the ethical standards of the 1964 Helsinki declaration and its later amendments. The Kaiser Permanente Northwest Institutional Review Board (IRB) approved this study and granted a waiver of informed consent. The IRB at the Centers for Disease Control and Prevention also approved the study.

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Sharma, A.J., Bulkley, J.E., Stoneburner, A.B. et al. Bias in Self-reported Prepregnancy Weight Across Maternal and Clinical Characteristics. Matern Child Health J 25, 1242–1253 (2021). https://doi.org/10.1007/s10995-021-03149-9

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  • DOI: https://doi.org/10.1007/s10995-021-03149-9

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