How women's gut health could affect their risk of preterm birth

Women's gut health may affect their risk of preterm birth, new research suggests.

Preterm birth can have many causes and risk factors, and researchers in China may have identified another one: the common gut bacterium Clostridium innocuum, or C. innocuum.

The bacterium produces an enzyme capable of degrading estradiol, an essential hormone for sustaining pregnancy – and in the study, women with C. innocuum present in their guts were at higher risk of giving birth early.

The study was published in the journal Cell Host & Microbe.

The findings, if confirmed in other research, point to women's gut microbiome as being a potentially important, and potentially modifiable, factor in the global effort to reduce preterm births.

“Preterm birth is a leading cause of death in newborns and children under five,” said An Pan, one of the study's authors and an epidemiology professor at Huazhong University of Science and Technology in China.

“This study suggests that for pregnant women or women preparing to become pregnant, it may be important to monitor their gut microbiome to prevent potential adverse pregnancy outcomes," Pan said in a statement.

What is preterm birth and what are the risks?

Babies born before the 37th week of pregnancy are considered preterm. Preterm birth can happen spontaneously or due to medical complications during pregnancy, according to the World Health Organization (WHO).

Causes of preterm birth can include infections, health issues such as diabetes, multiple pregnancies, and genetic factors, though in many cases no cause is identified, the WHO said.

Preterm birth, especially for babies born before 32 weeks, is associated with various health issues, including higher rates of death and disability, breathing problems, feeding difficulties, developmental delays, and problems with vision and hearing.

According to WHO, preterm birth complications are the leading cause of death among children under the age of five, causing approximately 900,000 deaths in 2019.

The agency said that three-quarters of these deaths could be prevented.

How the research was conducted and its caveats

The analysis drew on data from two large patient groups in China: the Tongji-Huaxi-Shuangliu Birth cohort, which included nearly 4,300 women in early pregnancy, and the Westlake Precision Birth cohort, which included more than 1,000 women in mid-pregnancy.

Researchers collected their stool and blood samples in order to examine their microbial composition, human genetic variation, and hormone metabolism.

The researchers were able to identify 11 groups of microbes and one distinct species associated with preterm birth. Among these, C. innocuum had the strongest link.

Further investigation revealed that this bacterium produces an enzyme that degrades estradiol, a form of oestrogen that is important to a healthy pregnancy.

“Estradiol regulates critical pathways that sustain pregnancy and initiate the process of childbirth,” Zelei Miao, one of the study's authors and a researcher at Westlake University in China, said in a statement.

“We propose that dysregulated estradiol levels induced by a high prevalence of C. innocuum could be the mechanism that links the gut microbiome to preterm birth," Miao added.

However, the study authors emphasised that their findings are based on cohorts from China, where preterm birth rates are relatively low, meaning the results may not directly apply to other groups.

The complex ecosystem of the gut microbiome can vary with diet, environment, and genetics, so the researchers would need to test their theory in a broad range of ethnically and geographically diverse groups to confirm their findings.