Changes in Gut Microbiota During Pregnancy

Written by
Dr Fathalla Ali, PHD Paediatrics


During the pregnancy period unique inflammatory and immune changes alter the maternal gut function and microbiota composition as the pregnancy advances. The pregnant woman’s gut microbiota undergoes significant changes throughout the period of pregnancy. During the first trimester, gut microbiota is similar to that of non-pregnant women, but the composition and structure is dramatically altered over the course of pregnancy especially in the third trimester (1,3). These changes are characterized by a significant depletion in the level of short chain fatty acid bacteria with anti-inflammatory activities, which is depleted in metabolic syndrome (2). This alteration contributes to the changes in the host immunologic and metabolic function, resembling changes seen in metabolic syndrome such as weight gain and insulin resistance. However, unlike metabolic syndrome, the change in the gut microbiota composition during the third trimester has a positive and important effect on pregnancy and contributes to the women’s healthy and fetus growth and development. For example, gut microbiota plays a vital role in weight gain during pregnancy through enhanced absorption of fatty acids and glucose and increase fasting-induced adipocyte factor secretion. Weight gain in pregnancy is important to provide the essential needs of the growing fetus (1). 

Pregnancy is also associated with a dramatic hormonal alteration resulting in unique inflammatory and immune changes that alter the composition and function of gut microbiota. Specific metabolic hormones such as insulin, gastric inhibitory polypeptide and adipokines were found to be associated with alteration in gut microbiota abundance among overweight and obese pregnant women. Additionally, estrogen and progesterone affect the composition of the gut microbiota through their impact on microbiota growth and metabolism. For example, pregnant women might become susceptible to Listeria Monocytogenes infection due to elevated level of estrogen and progesterone leading to adverse pregnancy outcomes, such as preterm birth or stillbirth (3).

  • In this study, vaginal, oral and gut samples were collected from 42 pregnant and 18 non-pregnant women, and the microbiota composition was determined by using metagenome sequencing technology.
  • Results showed that the increased abundance of Lactobacillus was correlated with decreased abundances of Atopobium and Gardnerella in vaginal samples from pregnant women.
  • The increase in Lactobacillus colonization was attributed to the increased production of estrogen.
  • On the other hand, “in women with increased Gardnerella and/or Atopobium abundance, the vaginal mucosal site is hostile to Lactobacillus colonization, and therefore a favourable environment for dysbiotic bacteria growth”.
  • Additionally, results showed that there was an increase in the relative abidance of Ruminococcus and Akkermansia in the gut of pregnant women.
  • Ruminococcus is a short chain fatty acids (SCFA) producer that plays a vital role in maintaining the ability of the immune system to fight infection.
  • Increased Akkermansia in the gut microbiome of pregnant women found to be related to microbiota modulation, as this genus has been related to metabolic homeostasis changes (the state of steady internal, physical, and chemical conditions maintained by living systems) in obese and diabetic patients after diet or bariatric surgery.
  • Therefore, this could be a sign that these bacteria are involved in microbiota stability during pregnancy and could contribute to the improvement of female reproductive health.

Keywords: Microbiota, pregnancy, gut microbiota, vaginal microbiota


  1. Nuriel-Ohayon, M., Neuman, H., & Koren, O. (2016). Microbial Changes during Pregnancy, Birth, and Infancy. Frontiers in microbiology, 7, 1031. Click here.
  2. Haro, C., Garcia-Carpintero, S., Alcala-Diaz, J. F., Gomez-Delgado, F., Delgado-Lista, J., Perez-Martinez, P., Rangel Zuñiga, O. A., Quintana-Navarro, G. M., Landa, B. B., Clemente, J. C., Lopez-Miranda, J., Camargo, A., & Perez-Jimenez, F. (2016). The gut microbial community in metabolic syndrome patients is modified by diet. The Journal of nutritional biochemistry, 27, 27–31. Click here.
  3. Edwards, S. M., Cunningham, S. A., Dunlop, A. L., & Corwin, E. J. (2017). The Maternal Gut Microbiome During Pregnancy. MCN. The American journal of maternal child nursing, 42(6), 310–317. Click here.
  4. Sparvoli, L. G., Cortez, R. V., Daher, S., Padilha, M., Sun, S. Y., Nakamura, M. U., & Taddei, C. R. (2020). Women’s multisite microbial modulation during pregnancy. Microbial pathogenesis, 147, 104230. Click here
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