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The Vaginal Microbiome and Preterm Birth

Written by
Dr Fathalla Ali, PHD Paediatrics


Preterm birth is defined as “babies born alive before 37 weeks of pregnancy completed”. Every year, about 15 million babies are born prematurely worldwide and 1 in 10 families around the world are affected by the birth of preterm babies. More than 1 million of children born prematurely die as a result of prematurity complications. It is classified as the leading cause of deaths in newborn infants (babies in the first month of life) and the second leading cause of death after pneumonia in under-5 children (1). Most preterm births occur spontaneously. The cause of spontaneous preterm birth is often unknown, but the most common causes include multiple pregnancies, complication of pregnancy (diabetes, high blood pressure) and intrauterine infection. Other environmental factors, such as the state of the microbiome, are among the most contributors to preterm birth. Inflammation induced by microbes resulting from urinary tract infection, sexually transmitted diseases is thought to increase the risk of preterm birth (2).

  • A case-control study investigated the risk of spontaneous preterm birth due to vaginal microbiome.
  • Researchers sampled 94 women with spontaneous preterm birth [17 early (<34 weeks) and 77 late (34–36 weeks) preterm birth] as case, and 356 women as control with term delivery, to compare the relative abundance of bacterial communities and to identify the vaginal community state type in spontaneous preterm birth and full term deliveries.
  • Results identified 6 vaginal Communities State Type bacteria (CST): 4 communities dominated by Lactobacillius, 1 community dominated by non-Lactobacillus and 1 community dominated by vaginosis associated bacteria.
  • The risk of early spontaneous preterm birth decreased among women if their vagina was colonized with Lactobacillus and Bifidobacteria.
  • On the other hand, the risk of early spontaneous preterm birth increased among women their vaginal bacterial community dominated with vaginosis related bacteria such as Gardnerella vaginalis, Atopobium vaginae and Veillonellaceae bacterium.
  • Therefore, the state of altered vaginal microbiome or bacterial vaginosis could be associated with increased risk of early preterm birth.

Keywords: microbiome, vaginal microbiome, preterm birth, premature, Lactobacillus


  1. March of Dimes, PMNCH, Save The Children, WHO. Born Too Soon: The Global Action Report on Preterm Birth. Eds CP Howson, MV Kinney, JE lawn. World Health Organization. Geneva, 2012. Click here.
  2. Fettweis, J. M., Serrano, M. G., Brooks, J. P., Edwards, D. J., Girerd, P. H., Parikh, H. I., Huang, B., Arodz, T. J., Edupuganti, L., Glascock, A. L., Xu, J., Jimenez, N. R., Vivadelli, S. C., Fong, S. S., Sheth, N. U., Jean, S., Lee, V., Bokhari, Y. A., Lara, A. M., Mistry, S. D., … Buck, G. A. (2019). The vaginal microbiome and preterm birth. Nature medicine, 25(6), 1012–1021. Click here.
  3. Tabatabaei, N., Eren, A. M., Barreiro, L. B., Yotova, V., Dumaine, A., Allard, C., & Fraser, W. D. (2019). Vaginal microbiome in early pregnancy and subsequent risk of spontaneous preterm birth: a case-control study. BJOG : an international journal of obstetrics and gynaecology, 126(3), 349–358. Click here.

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