There are about 10 times as many bacteria living in our bodies as there are human cells. There are about 360 times as many microbial genes as human genes. Such statistics demonstrate the magnitude of the microbial impact on human health. Microbes alter metabolism, modulate immunity, degrade chemicals, and even affect the function of the brain. Optimizing microbial health during preconception, pregnancy, and the perinatal period has a powerful impact of the health of the pregnancy and the offspring, not only in infancy but also for their entire lives.