The first factor that comes to mind that could influence the colonization of the microbial community in newborn infants is if the mother is actively taking probiotics especially those that would directly affect the placental microbiota as that directly affects the developing fetus. I would think it is also good to keep the vaginal microbiota healthy as that would also be bacteria exposed to the infant as soon as they are born. During pregnancy the immune response also changes due to hormonal and metabolic changes designed to support the fetus, it is even more important to keep the mothers microbiome clean to prevent infections and inflammations that could compromise the mother and child. I think however after the child is born it is important to introduce bacteria into their microbiome such as letting them play outside in the mud and play on the floor sometimes to allow their immune response to build up. This is tricky though as they should also have their vaccines for certain life changing diseases and pathogens such as polio, whooping cough, and rotavirus. Another factor that can affect how well the mother can control her and her infant’s microbiota is their financial situation. Sometimes probiotics are too expensive to afford, and even a nice clean apartment or house with clean running water can be hard to come by which can have a direct effect on not just pathogens exposed to but also the overall health and immune response of both the mother and infant.