Introduction:
Low birth weight (LBW) is an important indicator of the healthy of the population and reflects the living conditions, health and health behaviours of pregnant women.

Objective:
To assess the relationship between Gross Enrollment Rate at the Tertiary Education Level, average salary, Gross Domestic Product per capita, unemployment, housing area, urbanization and low birth weight in Polish sub-regions.

Material and methods:
An ecological study was undertaken using data on socio-economic and demographic features and LBW in 2005–2014. The units of observation were 66 Polish sub-regions according to the NUTS-3 classification. Two models were used to assess the influence of SES variables on LBW incidence rate in a 10-year study period. The first was the Poisson regression model adjusted for density of population, which was followed by the multivariable model using the GEE method of model parameters estimation.

Results:
In Poland, significant slow changes in the LBW incidence rate were observed in 2005–2014 (AAPC = –0.44%/year). In model 1, the increase in LBW was associated with an increase in unemployment (1.005) and decrease of average salary (0.987), GERTEL (0.990) and housing area (0.991). In model 2, an unfavorable association was detected between the density of population (1.068) and a still existing relationship with unemployment (1.004), average salary (0.990) and GERTEL (0.991).

Conclusions:
Protective factors for newborns’ health were a higher level of education and income. The results indicate the need to take actions to reduce the risk factors of LBW among pregnant women living in densely populated areas.