A recent study has found no association between pre-pregnancy body mass index (BMI) and the risk of iron deficiency or anemia during pregnancy. The analysis, which utilized data from the National Health and Nutrition Examination Survey (NHANES) spanning 1999 to 2010, indicates that overweight and obesity before pregnancy do not alter iron status biomarkers, including serum ferritin, serum transferrin receptor (TfR), total body iron, and hemoglobin.
Lead researcher Dr. Rachel E. Walker from the Department of Nutritional Sciences at The Pennsylvania State University noted, “Despite the known correlation between pre-pregnancy obesity and adverse pregnancy outcomes, our findings suggest that pre-pregnancy weight does not affect iron deficiency or anemia.”
Iron deficiency and anemia are prevalent among women of reproductive age, with the risk of iron deficiency increasing from about 10% in non-pregnant women to up to 25% during pregnancy. These conditions are associated with higher risks of anemia, low birth weight, and infant mortality.
The rise in obesity rates among U.S. women of reproductive age has been linked to higher risks of Cesarean sections, gestational diabetes, and difficulties with breastfeeding. Previous research suggested that maternal BMI could influence iron deficiency due to changes in metabolism and inflammatory responses, particularly during pregnancy.
In this study, Walker and her team investigated the relationship between iron status and anemia across different pre-pregnancy BMI categories using NHANES data from 1,156 pregnant women aged 18 to 49. The chosen data cycles included information on iron status biomarkers, pregnancy status, gestational age, and self-reported pre-pregnancy weight.
Pre-pregnancy BMI was calculated from self-reported weight and height. Iron deficiency was defined as total body iron <0 mg/kg, while anemia was identified as hemoglobin <11 g/dL. The analysis employed weighted multiple linear regression models, both unadjusted and adjusted for age, race/ethnicity, education, and trimester.
Participants had an average age of 28 years, with nearly half reporting a normal pre-pregnancy BMI. The prevalence of iron deficiency, anemia, and iron deficiency anemia was found to be 14%, 8%, and 3%, respectively.
Although ferritin and total body iron levels appeared lower in women with normal and overweight pre-pregnancy BMI compared to those who were underweight or obese, these differences were not statistically significant (P > 0.10). No significant differences were observed in TfR or hemoglobin levels across BMI groups (P = 0.76).
Walker and colleagues concluded that pre-pregnancy BMI does not affect the prevalence of iron deficiency or anemia, with adjusted prevalence ratios for overweight (1.27; 95% CI, 0.89–1.82) and obesity (0.75; 95% CI, 0.39–1.45) showing no significant variation. Similarly, anemia prevalence did not differ significantly by overweight (1.08; 95% CI, 0.53–2.19) or obesity (0.99; 95% CI, 0.49–2.01) status.
The researchers emphasized the ongoing need for comprehensive national data collection on iron biomarkers during pregnancy to monitor progress in addressing maternal health disparities.
