How Bacteria in the Vagina Change During Pregnancy
Each piece of research reveals that most bacteria in the body are harmless and can live in almost any place they want, while having minimal impact on their host. Sometimes these bacteria are very helpful - they can prevent more harmful bacteria from entering places such as the stomach or throat. Sometimes they may go wild and get in places they shouldn’t, causing havoc.
Although the human body is a relatively secure and wealthy home, it has its downsides. The bacteria can experience seismological changes in their environment as the body grows, falls ill and changes. And for bacteria that live around the female reproductive areas, pregnancy represents a pretty major shift indeed.
Just to clarify, bacteria do not actually live in the womb (if they get inside there that can go very badly wrong) but they do set up camp along the vagina and basically any areas of the reproductive system (and indeed the body) that can be reached safely from the outside. As well as protecting against fungal and other pathogenic infections simply by colonising the available space, the vaginal bacteria also actively help to decrease the pH inside the vagina, making it harder for other infections to set up. As anyone with cystitis who took antibiotics will know, killing the bacteria can result in fungal infections thrush. The fungus can then take over if there is no bacteria.
In order to explore how the vaginal bacteria might change during pregnancy, researchers took 68 samples from 24 healthy pregnant women (between 18-40 confirmed weeks) and compared them to 310 samples from 60 non-pregnant controls. They isolated DNA from the vagina, sequenced it, and then organised it into different bacterial taxonomic groups. All the control women were non-menstruating at the time, and around half of them were taking hormonal contraceptives. Refer to 1. for more information.
Overall, pregnant women showed much less diversity in bacterial species and fewer colonies present, particularly in areas up near the uterus which were very sparse indeed. In both pregnant and non-pregnant women, colonies varied throughout the vaginal area, and the dominant species were Lactobacillus spp. Some particular bacterial species were found to be more prevalent in pregnancy, although the overall diversity was reduced. This snapshot of the vaginal bacteria flora as a changing landscape; affected by internal pH and decimated by oncoming pregnancy, is a fascinating one, showing a wonderful interaction between humanity and the bacteria that live inside them.
But pregnancy doesn't just involve changes in bacteria, it also comes with a baby! In the place where the foetus develops, there is comfort and safety. But suddenly it must be forced to descend a narrow and bacteria-laden tube and into a harsh and cold world. In a fascinating (although rather underpowered) study of infants born by either by vaginal birth or C-section, researchers did indeed find a difference in the bacterial communities. Vaginal birth babies had the typical vaginal bacteria such as Lactobacillus or Prevotella. Cesarean infants had the same species (Staphylococcus and Corynebacterium). Furthermore while in adults there are different bacterial species in different places (skin, gut, vagina, etc.) In the case of newborns, it was one bacterial species. It's not surprising that the newborns had only entered the world in a sterile environment. But it raises intriguing questions about how these different species manage to find their way into an infant's body and thrive in their respective niches.
Speaking as one of the many, many C-section babies out there I can't say my method of birth had a huge impact on overall health , or indeed my relationship with bacteria! What is certain is that bacteria will always be with us, growing to meet our needs and fluctuating throughout our lives.