The Rationale for Probiotics Improving Reproductive Health and Pregnancy Outcome


  • Jennifer N. S. Reid,

    1. University of Guelph, Guelph, ON, Canada
    2. Human Microbiology and Probiotics, Lawson Health Research Institute, London, ON, Canada
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  • Jordan E. Bisanz,

    1. Human Microbiology and Probiotics, Lawson Health Research Institute, London, ON, Canada
    2. Department of Microbiology & Immunology, The University of Western Ontario, London, ON, Canada
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  • Marc Monachese,

    1. Human Microbiology and Probiotics, Lawson Health Research Institute, London, ON, Canada
    2. Department of Microbiology & Immunology, The University of Western Ontario, London, ON, Canada
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  • Jeremy P. Burton,

    1. Human Microbiology and Probiotics, Lawson Health Research Institute, London, ON, Canada
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  • Gregor Reid

    Corresponding author
    1. Human Microbiology and Probiotics, Lawson Health Research Institute, London, ON, Canada
    2. Department of Microbiology & Immunology, The University of Western Ontario, London, ON, Canada
    3. Surgery, The University of Western Ontario, London, ON, Canada
    • University of Guelph, Guelph, ON, Canada
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Gregor Reid, Lawson Health Research Institute, F3-106, 268 Grosvenor Street, London, ON, Canada N6A 4V2.




Medical problems of most importance to reproductive health of women differ to some extent between the developed world and resource-disadvantaged countries. Nevertheless, many share a common link in microbial involvement.

Method of study

A review of the peer-reviewed literature on microbiota, probiotics, and reproductive health.


Indigenous and probiotic lactobacilli express properties antagonistic to pathogens, but complementary to host immunity. These organisms are associated with conception, reducing the risk of infection, as well as potentially lowering the risk of a number of complications of pregnancy that otherwise lead to maternal and infant mortality and morbidity.


The ability to manipulate the microbiome and to improve immunity through probiotics holds much promise. The lack of improvements over the past 40 years in managing urogenital infections in women is incomprehensible. Support for innovative diagnostic and treatment options is needed, including testing and implementing probiotic therapies, especially for women with poor access to healthcare and good nutrition.


At the core of human survival is the ability to reproduce. The health of the women is critical to this process. Studies have highlighted the adverse role that pathogenic microorganisms can have in preventing conception and birth of a healthy baby, but only relatively recently has there been an appreciation for the role of non-pathogens in a positive outcome.

Clinical and basic studies[1-4] covered by literature reviews[5, 6] have certainly highlighted the vast array of bacterial types that can be detected in the vagina and the importance of Lactobacillus dominance in most instances. Some differences exist between races, but these are more likely influenced by diet, menstrual status, sexual practices, socioeconomic status, and culture than host genetics.[7-12] The problems that women in the developed world perhaps view as most important, namely being able to conceive, avoid preterm labor and diabetes, and control the impact of infectious agents, are contrasted with those of resource-disadvantaged countries where women often die or suffer through violent acts, inadequate access to care, sexually transmitted infections including HIV, and their babies through birthing problems, malnutrition, and environmental challenges[13-17] (Fig. 1). Conscious of these contrasting priorities, this review will examine the basis for how probiotics (live microorganisms, which when administered in adequate amounts, confer a health benefit on the host)[18] could improve reproductive well-being, in developed and resource-disadvantaged countries, as well as mechanistic and clinical evidence in support of the potential.

Figure 1.

What are the key problems in reproductive health for which probiotics might help? (adapted from Esperanza de vida, Wikepedia).

The reproductive tract environment

Given the extreme complexity of human reproduction and the myriad of factors that could be detrimental to the outcome,[19] it is an amazing feat that most children are born healthy. The nature of the female reproductive environment is well known, but less appreciated may be the microbes that inhabit this area and their interaction with the host, fetus, and infant.

Humans have evolved from bacteria over millions of years, and the microbes are part of every stage of this evolutionary model, which of course require reproduction. The vagina, cervix, and uterus are exposed to bacteria, and the trillions of organisms in the intestine have access to the reproductive tract via the rectum and perineum. Thus, there is daily exposure of microbes to the reproductive tract, and it would be surprising if they could not influence the reproductive process from conception to end of gestation. Indeed, many infectious causes are known to prevent conception and terminate pregnancy. The common occurrence of vulvovaginal candidiasis (VVC), urinary tract infection (UTI), and bacterial vaginosis (BV), as well as other infections testifies to the microbial environment of this site.[20-23] However, the fact that infections are not even more commonplace is a reflection of an efficient immune system and other defense mechanisms, of which the indigenous microbiota is extremely important. Vaginal defenses include (i) mechanical barriers such as the mucus layer, hemocidin, fibronectin, (ii) host protective enzymes such as lysozyme and lactoferrin, and (iii) host immune responses including the complement system and secretory immunoglobulin A (IgA),[24-26] all of which are influenced by the microbiota.

Douching, which is more common in African and African American women than their Caucasian counterparts, oral and biomaterial-oriented contraception, sexual contact, menstruation, bathing, and feminine hygiene practices all influence the vaginal environment, including the microbiota.[27-30] But generalizations are difficult to make, because longitudinal studies have shown that the microbial profiles are remarkably stable in some women and very changeable in others.[9, 31]

Aberrations in the reproductive tract environment are associated with a range of adverse outcomes, including premature birth. These infants, and others with very low birth weight (≤1500 g), have a higher risk of significant and lifelong motor, cognitive, and behavioral dysfunction with many developing autism spectrum disorders (ASD) following chorioamnionitis and acute intrapartum hemorrhage.[32] Although the exact cause(s) of ASD remains to be found, maternal immune disturbances during pregnancy and systemic and cellular immune abnormalities have been described.[33] It is already known that gut bacteria and probiotic organisms, can indirectly affect the brain and behavior[34, 35] and immune-derived outcomes such as allergy. Once the baby is born, gut microbes have the potential to influence the severity of ASD and secondary sequelae.[36, 37]

The first 1000 days of life are critical for many reasons, not the least of which is survival.[38] There are clearly inequities in low-income countries[39] with poor access to food, healthcare and appropriate interventions, and in those living in areas where external factors, such as pollution, are poorly controlled.

Environmental influences on pregnancy

The adverse effects of alcohol, drugs, and smoking on the fetus have long been documented. Likewise, domestic support or abuse, sexually transmitted agents, and factors such as nutrition and exercise can all affect pregnancy and infancy outcomes. But damage due to environmental toxin exposure, while long recognized with lead poisoning, has more recently become a major issue especially in Bangladesh area where millions of people have been exposed to arsenic in the drinking water.[40] Maternal exposure to high concentrations of inorganic arsenic increases the risk of spontaneous loss of the fetus,[41] as well as risk of skin lesions, high blood pressure, diabetes mellitus, chronic disease, and all-cause infant and adult disease mortality.[42] The mode of action includes enzyme inhibition, oxidative stress, immune, endocrine, and epigenetic effects, and increased blood pressure and anemia during pregnancy.[43] Other toxic metals, such as cadmium, lead, and mercury, confer damage to the mother and embryo.[44-46]

Humans are exposed to a range of toxic compounds such as pesticides through food and air and acrylamide from cooking starchy food and contact with dyes, adhesives, contact lenses, cosmetics and skin creams, food packaging materials, and permanent press fabrics.[47, 48] Depending on the concentrations and accumulation, adverse effects on reproduction can occur. Rauch and Lanphear[49] reported that many disabilities of childhood have their roots in the environment including toxins in air, water, and food. Chemicals commonly found in plastics may have subtle but serious effects on child development, and many disabilities spring from the complex interplay of environmental risk factors and genetic susceptibility. Organochlorine pesticides in pregnant women may be considered as an important etiological factor in ‘idiopathic’ fetal growth restriction.[50] Early life intrauterine exposure to environmental toxins can have a profound and enduring impact on the neuroregulatory systems mediating violence and aggression.[51]

These problems are shared among developed and developing countries. Polychlorinated biphenyls and lead can increase attention-deficit/hyperactivity disorder, the most frequently diagnosed neurobehavioral disorder of childhood.[52] In human placenta, mercury concentrations of over 50 ng/g were found in China (Shanghai), Japan, and the Faroe Islands. Cadmium levels ranged from 1.2 ng/g to 53 ng/g and were highest in USA, Japan, and Eastern Europe. Lead showed the greatest variability, with levels ranging from 1.18 ng/g in China (Shanghai) to 500 ng/g in a polluted area of Poland.[53] In a study of 100 pregnant women from Hassleholm and Simrishamn in southern Sweden (collection period 2002–2003), the median values of total mercury (B-Hg 0.70 μg/L), cadmium (0.30 μg/L), and lead (11.0 μg/L) in whole blood and hair mercury concentrations (0.22 μg/g) were related to the number of fish meals per week and to the number of occlusal amalgam fillings (multiple r = 0.51; P < 0.001).[54] It is believed that levels of only 300 ng/g MeHg, as measured from the hair, have adverse affects on child neurological development.[55] In a sampling of women of reproductive age from Ontario Canada, 15% exceeded this limit.[56]

The rationale for probiotic interventions

In addition to environmental compounds, major causes of problems in pregnancy include diabetes, cardiovascular disease and infection and inflammatory processes. Sometimes these factors are interlinked. For example, there is a strong association between elective preterm delivery (usually undertaken because of growth restriction or preeclampsia) and ischemic heart disease.[57] It should be noted that probiotics have not been proven clinically to reduce the risk of these complications in pregnancy, but as presented in Table 1,[46, 58-72] there are a number of attributes of these organisms that could play a role. The in vitro and animal data accumulated so far would support clinical studies to assess the potential for probiotic interventions.

Table 1. Rationale for probiotics providing benefits in pregnancy
Factor increasing problems during pregnancyMechanisms by which probiotic organisms might interveneCitation
Infectious and inflammatory causes of preterm laborAbility of lactobacilli to displace and inhibit pathogens and modulate immunity, including TNFα, Cox-2, and prostaglandin dehydrogenase. Ability to cure bacterial vaginosis and reduce risk of recurrences.



Poor nutritional uptake and damaged gut epitheliumImproved gut barrier function64–67
Onset of preeclampsiaReduced risk of preeclampsia with intake of probiotics, potentially via a local modifying effect on placental trophoblasts and systemic inflammation.68
Exposure to environmental toxinsSequestration of toxic metals and degradation of pesticides and carcinogens.69 Figs 2, 3.
Maternal heart disease

Potential lowering of blood pressure and cholesterol.

Lactobacillus decreasing circulating leptins, causing smaller myocardial infarcts and greater recovery of post-ischemic mechanical function



The development of the fetus and diseases it contracts after birth and later in life can be significantly affected by maternal nutrition. Too little effort is made to prevent many chronic diseases, such as cardiovascular and metabolic, by providing girls and young women in developing and developed countries, with balanced and adequate diets.[73] With such an intervention, the health of hundreds of millions of people could be improved.

The gestational development of different cell types, tissues, and organ systems ultimately configures a healthy child or predisposes him/her to pathological conditions.[74] By week three of gestation, the central nervous system and heart are well along the developmental pathway. By weeks 14–16, the brain can control sucking, swallowing, and irregular breathing movements. Yet, while iron/folic acid supplements from early pregnancy to 3 months postpartum enhance working memory, inhibitory control, and fine motor functioning,[75] the influence of the maternal microbiome on the brain has not been studied. The human brain is nearly 60% fat. Essential fatty acids, particularly the omega-3 fatty acids (α-linolenic acid), are important for brain development during the fetal and postnatal period.[76] Lactobacilli can produce conjugated isomers of α-linolenic acid[77] as well as a range of neurochemicals.[78] Given the potential access of vaginal lactobacilli and their by-products to the uterus and placenta[79] and by-products via the bloodstream from the gut, it seems highly plausible that these species, and no doubt others, play a role in fetal development and/or programming. With the growing appreciation for gut–brain signaling and the impact of organisms on memory, anxiety, and other brain functions,[80, 81] studies of how microbes influence fetal development should become a priority.

Reports of probiotic lactobacilli being administered during pregnancy suggest that immune modulation may be feasible, for example, in reducing the risk of certain allergic responses.[82] The mechanisms involved in immune modulation by probiotic organisms have been studied by a number of groups. Recent articles have, for example, shown that L. reuteri 6475 histamine stimulated increased levels of cAMP, which inhibited downstream MEK/ERK MAPK signaling via protein kinase A and suppressed TNF production by transcriptional regulation.[83] This is interesting as TNF can be involved in induction of preterm labor. Another study has shown that lactobacilli modulate the regulation adherence junction proteins such as E-cadherin and β-catenin, important in epithelial barrier function.[84] Membrane integrity is critical for successful blastocyst formation and retention of the amnion, chorion, and placenta, so it will be interesting to determine the molecules produced by lactobacilli and to see whether they may also influence different membrane structures involved in pregnancy. As immune modulatory mechanisms of probiotic bacteria become identified,[85] efforts to manipulate the microbiota will become more targeted and clinically effective.

The only clinical study to examine whether probiotics might prevent preterm labor did not have a sufficiently large sample size to verify the hypothesis, even though the trend toward this was evident.[86] Future studies of probiotics in pregnancy should also consider the dangers of exposure to environmental toxins. Probiotic bacteria have the potential to bind to and/or degrade toxins (Figs 2, 3) and thereby reduce host uptake of these compounds, with potential benefits to mothers and their children.

Figure 2.

Atoms of the heavy metals lead (Pb), cadmium (Cd), and arsenic (As) bound per cell after incubation. Higher bars represent more atoms of the respective metals bound and removed from solution. (Error bars ± S.E.M). The binding assay was adapted in which the heavy metals were added to a 50 mm HEPES buffer at a concentration of 1 ppm (parts per million of the metals). The HEPES/metal buffer was either treated with lactobacilli (1 × 109 CFU/mL) or left as an uninoculated control.

Figure 3.

Pesticide concentration in supernatant post-Lactobacillus rhamnosus GR-1 incubation. Bar plot represents the concentration of pesticides (Malathion and Parathion) compared to the controls that are not bacterial treated.

Challenges with the transition to patients

A number of hurdles must be overcome before optimal application of probiotics can be achieved for reproductive health. The scientific rationale is strong and growing. The best animal models are sheep and pigs, but apart from testing recombinant probiotics or strains with no history of safe use in humans, and mechanistic investigations, it is not clear that animal studies are critical. As presented above, many probiotic studies have been performed in pregnant women, without any evidence of major side effects to the mother or fetus. However, regulatory agencies in the USA and Europe have been setting up a series of barriers that significantly hinder human studies. Because the vast majority of probiotics are delivered in foods and supplements, the regulatory systems will not permit any claims for disease prevention and treatment, irrespective of the failures of approved pharmaceutical agents and plight of patients. Thus, without the finances to develop probiotics as drugs, applications to pregnancy will be limited. Even if claims are not the issue, the FDA will still not permit foods being tested to prevent complications of pregnancy. To get around this studies could be performed outside of the USA or be designed with primary outcomes that are not specific to a disease.

These issues will become more pertinent as our knowledge of the human microbiome expands. For example, probiotics might be used to target oral Fusobacterium nucleatum, an organism recently detected in both neonatal gastric aspirates and maternal oral samples in cases of preterm birth from mothers presenting with localized periodontal pockets.[87] The realization that babies born by Cesarean section and those fed formula milk have different microbiomes than those born vaginally and fed human milk[7] could result in purposely colonizing Cesarean born infants with the mother's vaginal microbes or multispecies probiotic derived from them. The application of multistrain probiotics to improve pregnancy outcomes has already been tested in a pilot study, with some success in terms of modulating immune parameters and the vaginal microbiota,[88] while the addition of single probiotic strains to infant formula has been approved in many countries and has been reported to increase sIgA levels in the infant.[89]

If probiotic products are shown to reduce the risk of preterm labor, preeclampsia and/or gestational cardiovascular or metabolic diseases and to improve infant cognitive function and health, the implications are enormous. Maternal and newborn mortality and morbidity are massive issues and even if most cases are in the developing world, this does not negate the responsibility of scientists in other regions. On the contrary, given our resources, we should be making extra efforts to apply our findings to people who need them the most. The Bill and Melinda Gates Foundation has identified the critical importance of childhood cognitive function and has invested in studies designed to improve the function of millions of children in the developing world. But, more is required. The creation of community kitchens that produce probiotic yogurt in impoverished parts of Africa is another step in the right direction, but accessing 3000 people a day[90] needs to be translated to 3 million a day. Supporting the local research infrastructure that can study outcomes, overcome challenges, and improve effectiveness of the probiotics, prebiotics, or synbiotics is also essential for success and sustainability. Likewise, such initiatives should also be undertaken in developed countries where poverty and malnutrition are also major societal problems. This cannot be achieved without support from the public and private sectors. Time will tell whether such support ever comes to bare.


Our research is supported by the Bill and Melinda Gates Foundation, Canadian Institutes for Health Research (Vogue Team), and Groupe Danone and the Natural Sciences and Engineering Research Council of Canada.