Does asymptomatic carriage of streptococcus bacteria affect the course of pregnancy?

The majority of childbirths proceed without problems. In recent years, however, preterm deliveries, inductions of labour and caesarean sections have become increasingly common. They expose the mother and the newborn to complications, which often are due to infections. In order to prevent serious infections, we need research-based knowledge about, for example, the source of pathogens.

Published: 13.1.2022
Writer: Kirsi Gröndahl-Yli-Hannuksela


During pregnancy, a woman’s body undergoes great changes in preparation for carrying and protecting the growing foetus for nine months. Most pregnancies end up with a normal birth but, in recent years, preterm deliveries, inductions of labour and caesarean sections have increased to a significant extent. In these situations, the mother and the newborn are at an elevated risk of complications, which may jeopardize their well-being.

It is often assumed that there is an infection underlying the complication, although it is not always confirmed microbiologically. We know that infections are associated with premature births and that caesarean sections involve an elevated risk of infections, but even in these cases, the microbiological confirmation usually remains lacking as the necessary treatment is initiated without delay.

Globally, 5–10 percent of women in childbed suffer from puerperal infections and these infections are the sixth most common cause of death for mothers after childbirth. A major part of severe infection cases are found in low and middle income countries. In my own research, I focus on clarifying, in particular, where the mother gets the pathogen from – for example, whether she is already carrying the bacteria in her body asymptomatically. This is not at all rare since many bacteria are capable of living on human mucous membranes or skin without causing any type of symptoms.


A broad disease spectrum

My research focuses on streptococcus bacteria. Group A streptococcus (GAS, Streptococcus pyogenes) is one of the most common human pathogens. Of the broad range of diseases it causes, angina is probably the best known. GAS may also cause other more severe and even life-threatening diseases. On the other hand, GAS may reside in the throat without causing any infection or symptoms, which is referred to as asymptomatic carriage. Asymptomatic carriage plays a significant role in the spread of diseases, as GAS is transmitted through droplets.

GAS is also a generally known cause of childbed fever or puerperal sepsis. Puerperal sepsis is a rare but extremely serious infection that can develop immediately after childbirth, that is, during the childbed period. Infections caused by GAS affect primarily the mother, but they also have an indirect effect on the newborn baby. In puerperal infections, it is not always possible to identify the pathogen, since the treatment is usually initiated on the basis of clinical evidence without waiting for a microbiological confirmation.

Another significant human pathogen, group B streptococcus (GBS, Streptococcus agalactiae) may be transmitted from the mother’s birth canal to the newborn baby during delivery. In the worst case scenario, GBS may cause the newborn a serious septic infection. In Finland, over 20 percent of pregnant women are asymptomatic GBS carriers. In many countries, also in Finland, pregnant women are routinely tested for GBS during delivery and possible carriers are treated with antibiotics.  The aim is to prevent serious infections in newborn babies, in particular.


New information about risk factors

Our research group is initiating a project at the University of Turku to study the prevalence of asymptomatic carriage of GAS and GBS during pregnancy, the occurrence of co-carriage of GAS and GBS, and the role of carriage in terms of possible complications of the mother and the newborn. We also investigate the bacterial spread within the family.

Our research project will be carried out in close collaboration with researchers at the Department of Obstetrics and Gynaecology of Turku University Hospital. We will collect several samples from pregnant women and their partners for extensive analyses. In addition to the prevalence of asymptomatic group A and B streptococci, we will also study the antimicrobial susceptibility of these bacteria and carry out genome analyses of the bacterial strains. It is important to monitor the antimicrobial resistance, and our research will provide new knowledge about the current sensitivity of streptococcus bacteria. Moreover, we will follow up on the health of the mother and child over the first weeks after birth.

Our research will produce new information about the risk factors for possible complications during pregnancy or childbirth. The research results may also be helpful for assessing whether the present screening practices are sufficient. Our research design is completely new, and there are no reports on corresponding research conducted in Finland or elsewhere. We hope that the results of our research will help to prevent serious infections and, thus, promote the well-being of mothers, newborn babies and families.

The funding granted by the Sakari Alhopuro Foundation has significantly contributed to the implementation of the project in its planned extent.


Kuva kirjoittajasta



PhD, Adjunct Professor Kirsi Gröndahl-Yli-Hannuksela is working as a university teacher at the Institute of Biomedicine in the University of Turku. Her PhD thesis in 2015 dealt with whooping cough (pertussis) vaccination responses. Since then, she has been engaged in several clinical research projects. Her current research focuses on group A streptococcal (GAS) bacteria.





Picture: Shutterstock

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