I’ve written previously about one of my studies following new mothers and their newborn children which we did in collaboration with the obstetricians in one of the hospitals in Stockholm (Södersjukhuset). The research question was whether the placenta contains microbes or whether the baby is colonized with bacteria and other microbes through the birth process. A controversial issue that has been hotly debated among researchers.

Why would that be important to know?

When a baby is born, it comes in contact with the mother’s microflora from both the vagina and the intestinal opening. The child is immediately covered by bacteria and shortly there after, from the mothers skin and the environment as well. If the baby is born by caesarean section, it misses the first dose of these bacteria and comes into contact with only the species found on the skin or in the hospital environment.

Breast milk also contains bacteria. They are carefully selected in the intestine by the mother’s immune system and transported all the way to the mammary glands of the breasts so that the baby can get the bacteria it needs. In other words, breast milk is a probiotic drink.

The bacteria that colonize the gut and other parts of the body have an important influence on the baby’s health and development. Bacteria in the gut will first help the baby break down breast milk, and then adapt to the dietary change when other foods are introduced. The bacteria will also train the baby’s immune system so that it knows which bacteria are useful and which are dangerous. The immune system also learns what is body-specific and what is foreign, a process that is amiss in diseases such as eczema, allergies or asthma.

10 years ago, everyone thought that amniotic fluid and placenta were completely sterile in healthy pregnancies. In maternity care, it was assumed that an infection in the uterus was a common cause of premature birth. But since 2011, many articles have described bacteria in the amniotic fluid, placenta and intestines of healthy newborns. It was suggested that the body has a similar mechanism for the bacterial flora of the placenta as it has for the mammary glands, i.e., that it selects bacteria which begin to colonize the intestine of the unborn child. But, could that really be true?

At our research center, we started planning for a study to contribute to a piece of the puzzle and help answer this question in 2016. We contacted Eva Wiberg Itzel, who is the chief physician at the birth at Södersjukhuset and her doctoral student Irene Sterpu, together we designed the study. The following year, when we had received an ethical permit to conduct the study and planned all the steps in detail, 50 women who would give birth with planned caesareans and 26 women who gave a traditional birth were included. Eva and Irene took samples from the placenta, amniotic fluid and from the baby’s skin during childbirth. All samples were stored in a biobank at the hospital and transported to our lab for us to look for bacteria. Kind of like detective work, we examined the samples with different methods to find the bacteria’s DNA (this is how you study the bacterial flora today in laboratories). We also cultured bacteria from the placenta but found them mainly in the placentas that had come out through the vagina. When we could not find a microflora in the placenta, we tried to find an explanation and tested whether the placenta itself has antimicrobial properties, which prevent bacteria from growing there.

Now our study has been published and in it we find that although it does not seem to be completely sterile inside the stomach (which would be a little strange as there are microbes everywhere) but that most bacteria that enter the placenta and amniotic sac can not grow there. Our conclusion is that although the placenta may contain low levels of some bacteria, the study convinced us that colonization mainly takes place after birth. This does not mean that the child is completely unprepared to face bacteria – via the blood, the unborn child’s immune system may also have encountered parts of bacteria that have begun to train the immune system. But that’s another story I can return to later.

It took our research group and our clinical partners almost 4 years from thinking about the issue to having our study reviewed and published. On Friday, December 11, Irene will defend her dissertation. We have to wait until the pandemic is over, we researchers have patience.

The publication of our study in its entirety can be found here.

If you are pregnant before week 19 and want to contribute to our SweMaMi study, we have extended the recruitment until 15 January. Info at www.swemami.se

Watercolor: Ina Schuppe Koistinen

This is a guest post. Any opinions expressed are the writer’s own.