Your baby's gut microbiome

The microbiome is the community of microbes that live in and on the body. Most are bacteria. They live on the skin, in the mouth and above all in the gut.

Good bacteria help digest food. They train the immune system to tell harmless microbes from harmful germs. They take up space so harmful germs have less room to settle.

A baby’s microbiome is simple at first. It changes a lot in the first months, then again when solid foods start. Around the age of 2 or 3, it starts to look more like an adult’s.

The gut fills with bacteria mostly from birth onward. Each step of the first days adds some.

• During a vaginal birth, the baby meets the mother’s bacteria. After a caesarean, the first bacteria come more from the skin and the hospital. The mix is different at first. A caesarean is often the right and safe choice, and the gut adapts with time.
• Holding your baby skin to skin on your bare chest passes your skin bacteria to your baby. Start as soon as you can after birth, whatever the type of birth.
• The first milk, called colostrum, carries live bacteria, antibodies and other protective factors. A first breastfeed in the first hour gives your baby all of this early.

Breast milk contains special sugars called human milk oligosaccharides. Your baby cannot digest them. They reach the gut intact. There they feed good bacteria, especially a family called bifidobacteria.

These bacteria then keep the gut slightly acidic. This makes life harder for harmful germs. Breast milk also carries antibodies that help protect against common infections.

A breastfed baby has fewer kinds of bacteria in the gut than a formula-fed baby. This is healthy, because the milk feeds mostly the bacteria that protect.

If you give both breast milk and formula, each feed of breast milk still helps.

For premature babies, the mother’s own milk is the first choice. Donor milk comes next, then formula. Your milk protects the fragile gut of a premature baby.

Some things change the first bacteria of the gut:

• Antibiotics kill harmful bacteria and good bacteria. The gut usually recovers, but it takes time. Longer courses have a bigger effect.
• Premature babies often need antibiotics and spend weeks in hospital. Their gut takes longer to settle.
• A caesarean birth changes the first mix, as explained above.

Antibiotics save lives. When your baby needs them, they come first.

Antibiotics do not work on viruses. Most colds, coughs and sore throats in children are caused by viruses. Do not ask for antibiotics your child does not need.

• Hold your baby skin to skin, often, from the first hours.
• Breastfeed if you can, or give expressed breast milk.
• If you breastfeed, eat a varied diet with plenty of fiber, fruits, vegetables and legumes.
• Give antibiotics only when a doctor prescribes them. Give the full course as prescribed. Never use leftover antibiotics.
• When solid foods start, offer a variety of vegetables, fruits and grains.

Research on the microbiome is still young. Many products claim to fix or boost a baby’s gut. For a healthy baby, there is no proof that they are needed. Do not give supplements or drops for the gut without asking your doctor. Some can be harmful for premature or sick babies.

You may read about wiping a baby born by caesarean with the mother’s vaginal fluid. This is not recommended outside research studies. It can pass on infections.

Call your doctor if your baby:

• has many watery stools a day, or blood in the stool
• has fewer wet diapers, a dry mouth or no tears
• vomits often, or vomits green
• has a swollen, hard or painful belly
• has severe diarrhea during or after antibiotics
• is under 3 months and has a temperature of 38 °C or higher

Call the Red Cross on 140 if your baby is very hard to wake, floppy, or struggles to breathe.