Iron status in a representative sample of US pregnant women is not associated with pre-pregnancy BMI: results from the NHANES (1999-2010) study

Iron deficiency in pregnancy is related to many poor health outcomes, including anemia and low birth weight. A small number of previous studies have identified maternal body mass index (BMI) as potential risk factors for poor iron status. Our objective was to examine the association between pre-pregnancy BMI and iron status in a nationally representative sample of US adult women. We used data from the National Health and Nutrition Examination Survey (NHANES; 1999-2010) for pregnant women ages 18-49 years (n=1156). BMI (kg/m2) was calculated using pre-pregnancy weight (self-reported) and height (measured at examination). Iron deficiency (ID) was defined as total body iron (calculated from serum ferritin and transferrin receptor using Cook’s equation) < 0 mg/kg and anemia as hemoglobin < 11 g/dL. Associations were examined using weighted Poisson regression models, adjusted for confounders (age, race/ethnicity, education, family income, and trimester). Approximately 14% of pregnant women had ID and 8% had anemia in this sample. There were no differences in the prevalence of ID or anemia in women with pre-pregnancy overweight and obesity (ID: overweight, adjusted prevalence ratio (PR)=1.28, 95%CI: 0.89-1.83; obesity, PR=0.75, 95%CI: 0.39-1.45; anemia: overweight, PR=1.08, 95%CI: 0.53-2.19; obesity, PR=0.99, 95%CI: 0.49-2.01) compared to women with a normal BMI. Findings from these US nationally representative data indicate that iron status in pregnancy does not differ by pre-pregnancy BMI. Since iron deficiency during pregnancy remains a significant public health concern, NHANES should consider measuring current iron status in upcoming cycles. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement Yes ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Not Applicable The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The original NHANES protocol was approved by the National Center for Health Statistics’ Research Ethics Review Board. The current study accessed only deidentified publicly available data. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Not Applicable I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Not Applicable I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Not Applicable The NHANES data underlying the results presented in the study are publicly available for download from the NHANES database (https://www.cdc.gov/nchs/nhanes/index.htm).