Association between air particulate matter pollution and blood cell counts of women preparing for pregnancy: Baseline analysis of a national birth cohort in China

Background: Limited evidence is known about whether long-term exposures to air borne particulate matters of 2.5 μm or less (PM_2.5) impact human hematologic index for women preparing for pregnancy. No study assessed the effect of PM₁, which is small enough to reach the blood circulation.

Objective: To evaluate whether exposure to PM₁ and PM_2.5 is associated with blood cell count of woman preparing for pregnancy.

Method: Based on the baseline data of a national birth cohort in China, we analysed the white blood cell (WBC), red blood cells (RBC) and thrombocyte counts of 1,203,565 women who are aged 18-45 years, being Han ethnicity, had no chronic disease and preparing for pregnancy. We matched their home addresses and examination date with daily concentrations of PM₁ and PM_2.5 which were estimated by a machine learning method with remote sensing, meteorological and land use information. Generalized additive mixed model to examine the associations between exposure to one-year average exposure to PMs prior to the health examination and the blood cells counts, after adjustment for potential individual variables.

Results: A 10 μg/m³ PM₁ increment was associated with -1.49% (95%CI: 1.56%, -1.42%) difference in WBC count; with 0.33% (95%CI: 0.30%, 0.36%) difference of RBC count; and with 1.08% (95%CI: 1.01%, 1.15%) difference of thrombocyte count. For PM_2.5, the corresponding difference was -0.47% (95%CI: 0.54%, -0.39%) for WBC; was 0.06% (95%CI: 0.03%, 0.09%) for RBC; and was 1.10% (95%CI: 1.02%, 1.18%) for thrombocyte. Women working as workers, being overweight and with tobacco smoking exposure had higher associations between PMs and hematologic index than their counterparts (p < 0.05 for interaction test).

Conclusion: Long-term exposure to PMs were associated with decrement in WBC, as well as increment in RBC and thrombocytes among Han Chinese women preparing for pregnancy. Measures such as using air purifiers and wearing a mask in polluted areas should be improved to prevent women from the impact of PMs.