Maternal Child Health and Environmental Exposures.

Maternal Maternal Child Health and exposure to environmental factors pose many threats to the maturing fetus. Chemical exposures can influence the individual as soon as he or she is conceived. As the zygote undergoes mitosis (cell division), the new cells themselves become part of the mother's environment, and through their particular physical and chemical influence they guide and control the development of further new cells. Different genes are activated or suppressed in each cell, so that while one group of cells is developing into brain tissue, another is giving rise to the heart, another to the lungs, and another to the skeletal system. Meanwhile, the lump of cells is surrounded by the larger environment of the mother's uterus, and this environment is surrounded by the mother and the world in which she lives.

Reference: 
http://social.jrank.org/pages/515/Prenatal-Development-Prenatal-Environmental-Influences.html
http://www.epi.umn.edu/mch/resources/hg/hg_enviro.pdf
http://www.minddisrupted.org/documents/Mind%20Disrupted%20report.pdf