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 Cooks 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.