Introduction and objective:
The results of epidemiological studies indicate that the higher maternal exposure to air pollution, especially with particulate matter during pregnancy, the lower the infant’s birth weight. The aim of this study was to estimate entire pregnancy and trimester-specific exposure of pregnant women in the city of Krakow, southern Poland, to fine particulate matter [≤10 µg (PM10)], and to assess its effect on the birth weight of boys and girls separately.

Material and Methods:
The study group consisted of 85,000 singleton, live, full-term births in Krakow city during a 15-year period (data from the birth registry). The mean concentrations of the pollutant for each month of gestation were estimated using continuous municipal monitoring data.

Results:
Multiple linear regression analyses indicated that the mean PM10 concentration during entire pregnancy was inversely associated with birth weight in girls and the group of boys and girls combined, after adjusting for maternal age, gestational age and year of birth; in boys the relationship was not statistically significant. Maternal exposure to PM10 during the first trimester was negatively associated with birth weight separately in girls and boys, and the group of boys and girls combined. However, the PM10 exposure during the second and third trimester of pregnancy was not associated with birth weight.

Conclusions:
PM10 air pollution at levels currently encountered in Krakow city adversely affect infant birth weight; however, the effect seems to be very small. The influence of particulate air pollution on foetal growth in early gestation is one of several possible explanations for the results, but further research is needed to establish possible biological mechanisms explaining the observed relationship.