(P19-025-24) Associations Between Heat Exposure in Early Pregnancy and Anemia, Inflammation and Iron Status Among Women in Rural Pakistan

Objectives: Heat stress during pregnancy has detrimental effects on obstetric and neonatal outcomes. However, the impact of heat on anemia in pregnancy has not been studied systematically. We examined associations between ambient temperature and anemia and iron status in the first trimester.

Methods: This was a secondary analysis from the Women First Trial conducted in Thatta, Pakistan where chronic maternal malnutrition and exposure to heat stress are common. Maternal hemoglobin (Hb) and pregnancy outcomes were available for 409 women. Serum samples were collected at 12 weeks of pregnancy (n = 181) and levels of C-Reactive Protein (CRP), α1-acid glycoprotein (AGP), ferritin and soluble transferrin receptor (sTfR) were measured. Temperature data were retrieved from using the GSDOR package. Multiple linear regression and structural equation models were utilized to assess relationships between anemia (Hb < 11g/dL), iron status and inflammation markers and average daily maximal temperature (T_max) or number of days >39°C (d>39°) in the first trimester.

Results: In linear regression models adjusting for covariates, Hb levels at 12 wks were negatively associated with T_max (ß/CI -0.03 g/dL, -0.07 – 0.00, p=0.06) and d>39° (ß/CI -0.01 g/dL, -0.02 – 0.00, p=0.01). Likewise, sTfR-F index was positively associated with d>39° (ß/CI 1.15, 0.28 – 2.03, p=0.01). Logistic regression for anemia status showed significant positive association with d>39° (OR 1.01, p = 0.04). Associations of T_max with Hb or sTfR-F index were attenuated to the null when including CRP and AGP in the models, while associations of d>39° with sTfR-F index remained highly significant (ß/CI 1.21, 0.33 – 2.09, p=0.007). Finally, structure equation modeling indicated a negative associations between Hb levels and T_max & CRP levels, and a positive association between T_max and CRP levels.

Conclusions: Collectively, the findings indicate that in the setting of chronic malnutrition, ambient temperature and especially exposure to high heat ( >39°C) is associated with lower hemoglobin and greater anemia risk. The findings are consistent with heat-associated inflammation contributing to this risk. Larger prospective studies are warranted to clarify effects of temperature on iron status and anemia in pregnancy.

Funding Sources: Bill & Melinda Gates Foundation, NIH/NICHD/ODS