Pregnant women living in large cities are more likely to give birth to higher weight babies than those living in rural areas, due to a higher exposure to xenoestrogens, a type of environmental pollutants that act like hormones, researchers have found. This is the first research study conducted in Spain establishing a correlation between estrogenic burden in pregnant women's placenta and a higher birth weight. For the purpose of this study, the University of Granada researchers examined two groups of pregnant women. The first group was composed of pregnant women living in Madrid working in the field of administration or education, while the second consisted of women living in rural areas of the province of Granada who were exclusively devoted to household chores. The researchers found that there were biological, demographic and socio-economic differences between both groups of women, which determined the presence of xenoestrogens in the placenta due to exposure to environmental chemicals. The researchers examined the factors conditioning environmental exposure, and a correlation was found between anthropometric and socio-demographic factors, health status, lifestyle and working conditions, and the total estrogenic burden. They found that the estrogenic effect of placental tissue extract is directly related with certain characteristics in parents, childbirth and newborn babies. Thus, the group with higher estrogenic effect of placental tissue extract in alpha fraction was that of older women with lower body mass index and living in Madrid. Additionally, this is the group, which gave birth to higher weight infants. These results suggested that estrogenicity of xenostrogens directly affects embryo-fetal development.