The Importance of Infants’ Exposure to Microorganisms

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Many studies have strongly suggested that the trillions of microorganisms that inhabit the human body influence our current and future health and may account for the rising incidence of several serious medical conditions now plaguing Americans, young and old.

The research indicates that cesarean deliveries and limited breast-feeding can distort the population of microorganisms in a baby’s gut and may explain the unchecked rise of worrisome health problems in children and adults, including asthma, allergies, celiac disease, Type 1 diabetes and obesity. These conditions, among others, are more likely to occur when an infant’s gut has been inadequately populated by health-promoting bacteria.

A growing number of researchers and consumers are now paying more attention to where it all begins, especially how this huge population of microbes in our bodies, called the microbiome, is affected, for good or bad, by how babies are born and nourished.

As this still-evolving information trickles down to prospective mothers, it could — and perhaps should — lead to profound changes in obstetrics, pediatrics and parenting. The two most important would be fewer scheduled cesarean deliveries and more mothers breast-feeding exclusively for six months to enhance the kinds and amounts of bacteria that inhabit an infant’s gut.

These organisms perform important functions that include digesting unused nutrients, producing vitamins, stimulating normal immune development, countering harmful bacteria and fostering maturation of the gut.

A disruption in one or more of these functions can lead to serious, sometimes lifelong, health problems. If, for example, gut maturation is impaired or delayed, some experts believe undigested proteins could leak into the bloodstream and trigger an allergy or gluten intolerance, or an impaired immune system could result in an autoimmune disorder like Type 1 diabetes, juvenile arthritis or multiple sclerosis.

Babies are exposed to some organisms in utero, but the organisms encountered during birth and the first months of life have the greatest influence on those that become permanent residents in their guts. Recent studies have shown that both a vaginal birth and exclusive breast-feeding can significantly affect the kinds and numbers of their gut microbes and the risk of developing various health problems.

For example, a Danish study of two million children born between 1977 and 2012 found that those born by cesarean delivery were significantly more likely than those born vaginally to develop asthma, systemic connective tissue disorders, juvenile arthritis, inflammatory bowel disease, immune deficiencies and leukemia.

Babies born vaginally primarily acquire the microbes that inhabit their mother’s vagina and bowel. However, those delivered surgically before membranes rupture and labor begins acquire microbes mainly from the mother’s skin and the personnel and environment in the newborn nursery.

When an emergency cesarean is performed after membranes rupture and labor has begun, the baby acquires fewer of the mother’s microbes than it would during a vaginal birth but many more than from a scheduled cesarean.

These differences in the gut microbiota were found to persist in children until at least 7 years of age, according to a study in Finland published in 2004.

Currently, about one baby in three in the United States is delivered by cesarean section, up from about one in five in the 1990s. Certainly, a surgical delivery can be lifesaving when, for example, the fetus or the mother is at risk of a serious or fatal complication from a vaginal delivery.

But other reasons for the rise in cesarean deliveries, including the readings from a fetal monitor, are less clear-cut. Even though many babies with borderline readings would be likely to be fine with a vaginal birth, women and their doctors are usually unwilling to take a chance when the monitor suggests that the fetus may be in trouble. And women who have one cesarean, which weakens the uterine wall, are more likely to have a second or third rather than risk a uterine rupture during subsequent labor and delivery.

To counter the effects of a surgical birth on the infant’s microbiome, a growing number of women whose babies are delivered by cesarean are requesting that medical staff transfer microbes from the mother’s vagina to their infants soon after birth. Some are administering the microbe exchanges themselves. However, an expert committee of the American College of Obstetricians and Gynecologists recently warned that the practice, known as vaginal seeding, was premature and possibly hazardous.

“At this time, vaginal seeding should not be performed outside the context of an institutional review board-approved research protocol until adequate data regarding the safety and benefit of the process become available,” the committee concluded. The committee cited a potential risk of transferring pathogenic organisms from the woman to the neonate.

If vaginal seeding is being considered, women should be informed of the risks and tested for infectious diseases and potentially pathogenic bacteria, including group B streptococci, herpes simplex virus, chlamydia and gonorrhea, the committee stated.

Dr. Suchitra Hourigan, a pediatric gastroenterologist and director of the Inova Translational Medicine Institute in Falls Church, Va., is planning a three-year study of 800 babies delivered by a scheduled cesarean, half of whom will get vaginal seeding, to help determine if the technique is safe and beneficial.

Dr. Hourigan said in an interview, “Women shouldn’t do vaginal seeding until trials show it’s safe and offers health benefits to infants. I’m worried about mothers doing this without screening and sometimes without supervision by a physician who says it’s O.K.”

She added that at the moment, breast-feeding is the best and safest way to expose babies born by cesarean to their mother’s bacteria. Breast milk contains many of the same beneficial bacteria found in a woman’s vagina, and breast-feeding infants are less likely than those consuming formula to develop respiratory and gastrointestinal infections and allergies as well as chronic diseases like diabetes, obesity and inflammatory bowel disease.

In a study published online last May in JAMA Pediatrics, researchers reported that babies who got all or most of their milk from the breast had microbiota most like their mothers’.

Dr. Grace M. Aldrovandi of the University of California, Los Angeles, and co-authors noted that “breast milk bacteria that seed the gut first influence and select for bacteria that follow, leaving a footprint that can be detected even in adulthood.” These organisms are associated with a reduced risk of developing asthma, they wrote.

However, infants in the study who were not primarily breast-fed acquired an abundance of bacteria linked to a risk of becoming obese. Some studies have found that “even small amounts of formula supplementation” can shift the microbiota away from a breast-fed pattern.