Human milk is a wonder to behold, providing for an impressive array of benefits in breastfed babies and children through its thousands of components. Breast milk is so intricate that researchers are still discovering new secrets to this nutrition-optimizing, immune-boosting, and growth-promoting substance.

But babies, it turns out, don't need to be born to start benefiting from one of breast milk's most abundant ingredients. A new study shows that a complex carbohydrate previously thought unique to breast milk is actually present in the womb.

A prebiotic, human milk oligosaccharides (HMOs) contribute to the development of the gut microbiome. A healthier collection of good bacteria in the large intestine translates into an overall better-functioning immune system, lifelong. Each one of us has a gut microbiome specific to the microbes we've been collecting and nurturing since we were babies.

Related: Behind the Tantrum: How the Toddler Microbiome Influences Behavior

Breastfeeding is among the key ways that a healthy gut microbiome is established, largely due its high level of HMOs.

Researchers are increasingly discovering that unborn babies are exposed to HMOs as early as the first trimester. Previous studies detected HMOs in the urine and blood of pregnant women.

This latest study found, for the first time ever, that HMOs circulate in the amniotic fluid.

"[This] opens up an entirely new field of research and expands the HMO focus throughout development and after birth," said Dr. Lars Bode, associate professor of pediatrics at the University of California's School of Medicine in San Diego.

The scientific thought is that HMOs must influence the early gut microbiome even while the unborn baby is still developing. Dr. Bode also speculates that amniotic HMOs may protect against preterm birth:

"HMOs could also potentially be involved in prenatal lung or brain development. We don't know yet how early during pregnancy HMOs appear in the amniotic fluid, but imagine if we could screen HMOs in amniotic fluid as a marker for preterm delivery risk?"

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