Pre-Pregnancy BMI Unrelated to Iron Deficiency During Pregnancy, Study Finds

Women with pre-pregnancy overweight or obesity did not exhibit an increased risk for iron deficiency or anemia during pregnancy, compared with normal pre-pregnancy weight, according to the results of a new analysis.¹

Based on data from the National Health and Nutrition Examination Survey (NHANES) 1999-2010 cycle, pre-pregnancy overweight and obesity status demonstrated no difference in iron status biomarkers, including serum ferritin, serum transferrin receptor (TfR), total body iron, and hemoglobin.

“Although pre-pregnancy obesity is strongly linked to increased risk of adverse pregnancy outcomes, based on our results, it was not associated with iron deficiency or anemia,” wrote the investigative team, led by Rachel E. Walker, PhD, department of nutritional sciences, The Pennsylvania State University.

Both iron deficiency and anemia are common among women of reproductive age – iron deficiency risk increases from approximately 10% in non-pregnant women to up to 25% during pregnancy.² The presence of iron deficiency during pregnancy has been linked to an elevated risk of anemia, low birth weight, and infant mortality.³

Obesity is on the rise in the US population, including women of reproductive age – pre-pregnancy obesity has been linked to an elevated risk of Cesarean section, gestational diabetes, and failure to initiate breastfeeding.⁴ According to prior evidence, maternal body mass index (BMI) may put women at risk for the development of iron deficiency, due to alternations in metabolism and inflammatory signaling, particularly during pregnancy.

In this analysis, Walker and colleagues examined the link between iron status and anemia by pre-pregnancy BMI category using NHANES data on pregnant women aged 18–49 years (n = 1156) in the US.¹ The 1999-2010 cycles were selected because they contained data on iron status biomarkers, pregnancy status, gestational age, and self-reported pre-pregnancy weight.

Pre-pregnancy BMI was calculated using the self-reported weight and height, measured at the time of examination. Iron deficiency was categorized as total body iron <0 mg/kg, a calculation using serum ferritin and TfR using Cook’s equation. Anemia was defined as hemoglobin <11 g/dL.

For the primary analysis, the associations between iron biomarker concentrations and BMI were evaluated using weighted multiple linear regression models. All regression models were run unadjusted and adjusted, for age, race/ethnicity, education, and trimester.

Participants had a mean age of 28.0 years, with nearly half reporting a normal pre-pregnancy BMI. Upon analysis, the prevalence of iron deficiency, anemia, and iron deficiency anemia was 14%, 8%, and 3%, respectively, in the population.

Ferritin and total body iron concentrations trended lower in women with pre-pregnancy BMI in the normal and overweight categories, compared with the underweight and obese categories, but the differences did not achieve statistical significance (P >.10). No statistical or meaningful differences were identified between BMI groups in TfR or hemoglobin (P = .76).

Overall, Walker and colleagues found no difference in the prevalence of iron deficiency by pre-pregnancy BMI status, including overweight (adjusted prevalence ratio [PR], 1.27; 95% CI, 0.89–1.82) and obesity (PR, 0.75; 95% CI, 0.39–1.45). They additionally observed no differences see in the prevalence of anemia by overweight (PR, 1.08; 95% CI, 0.53–2.19) or obesity (PR, 0.99; 95% CI, 0.49–2.01) status.

“Given these results and the fact that prenatal iron deficiency remains a significant public health concern, there is a need to continue collection of high-quality national data on these biomarkers during pregnancy to assess progress over time in alleviating maternal health disparities,” they wrote.

References

1. _{Ciulei MA, Gallagher K, Ba DM, et al. Iron status and anemia in a representative sample of US pregnant women is not associated with pre-pregnancy BMI: Results from the NHANES (1999-2010) study. PLoS One. 2024;19(9):e0300912. Published 2024 Sep 10. doi:10.1371/journal.pone.0300912}
2. _{Gupta PM, Hamner HC, Suchdev PS, Flores-Ayala R, Mei Z. Iron status of toddlers, nonpregnant females, and pregnant females in the United States. Am J Clin Nutr. 2017;106(Suppl 6):1640S-1646S. doi:10.3945/ajcn.117.155978}
3. _{Sundararajan S, Rabe H. Prevention of iron deficiency anemia in infants and toddlers. Pediatr Res. 2021;89(1):63-73. doi:10.1038/s41390-020-0907-5}
4. _{Wawer AA, Hodyl NA, Fairweather-Tait S, Froessler B. Are Pregnant Women Who Are Living with Overweight or Obesity at Greater Risk of Developing Iron Deficiency/Anaemia?. Nutrients. 2021;13(5):1572. Published 2021 May 7. doi:10.3390/nu13051572}