In an article published in the journal Current Opinion in Microbiology, scientists have provided a detailed overview of the factors affecting maternal gut microbiota during pregnancy and its impact on maternal and infant health.
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Pregnancy is associated with a wide range of hormonal, immunological, and metabolic changes needed for fetal development. The most notable changes include increased cardiac output, higher levels of T regulatory cells, and alteration in gut microbiome composition.
Alteration in gut microbiota composition and diversity is associated with changes in women's metabolic, immunological, and neurological processes, irrespective of pregnancy status. In addition, changes in gut microbiota composition are known to affect insulin sensitivity. In children with type 1 diabetes, functional and metabolic changes in gut microbiota have been documented.
Alteration in gut microbiota during pregnancy
Only limited evidence is available to thoroughly understand the changes in gut microbiota during pregnancy and its impact on maternal and fetal health. However, according to the available literature, low-grade inflammation at the intestinal mucosa as well as hormonal changes, might be responsible for gut microbiota alteration during pregnancy.
Regarding hormonal changes, pregnancy-related induction in progesterone levels is known to directly associate with increased Bifidobacterium levels in women. Bifidobacterium is a beneficial bacterium that naturally resides in the intestine. Therefore, the gut-to-gut transmission of this bacterium from the mother to the infant is crucial during the neonatal period. In infants, this bacterium helps degrade human milk oligosaccharides coming from maternal milk, in addition to developing infant gut microbiota and immune system.
Factors influencing maternal gut microbiota during pregnancy
Adult human gut microbiota can be influenced by many factors, including body mass index (BMI), medications, diseases, environment, and lifestyle (diet, physical activity, smoking, and drinking habits). Pre-pregnancy exposure to these factors can lead to structural and functional alteration in maternal gut microbiota during pregnancy.
Animal studies have shown that maternal diet influences maternal and infant gut microbiota composition before and during pregnancy. Both pre-pregnancy body weight and pregnancy-related weight gain have been found to alter the composition and diversity of maternal gut microbiota.
Infant gut microbiota are influenced by the way they are delivered. For example, infants delivered vaginally have been shown to gain beneficial changes in gut microbiota compared to those delivered by c-section.
Functional studies in animals have shown that smoking-related nicotine exposure during pregnancy affects maternal gut microbiota, which in turn alters fetal exposure levels to circulating short-chain fatty acids and leptin during in-utero development.
Certain diseases before pregnancy, such as inflammatory bowel disease, have been found to influence maternal microbiota during pregnancy. The microbiota of the pregnant mother's gut has also been shown to be affected pre-pregnancy and during pregnancy by certain medications, including antibiotics, proton-pump inhibitors, metformin, laxatives, and probiotics.
Maternal health impact of altered gut microbiota
Studies have found maternal gut microbiota alteration during pregnancy is associated with pregnancy complications, including gestational diabetes and preeclampsia.
A spontaneous induction in blood glucose levels during pregnancy is medically termed gestational diabetes. Studies have shown that a reduced abundance of beneficial bacteria and an increased abundance of pathogenic bacteria are responsible for the onset of gestational diabetes.
In the microbiome of gestational diabetes patients, an increased abundance of membrane transport, energy metabolism, lipopolysaccharides, and phosphotransferase system pathways has been observed. Recent evidence indicates that gut microbiota-derived dopamine deficiency in the blood, impaired production of short-chain fatty acids, and excessive metabolic inflammation are collectively responsible for the development of gestational diabetes.
Preeclampsia is characterized by new-onset hypertension, proteinuria, and organ dysfunction during pregnancy. Studies involving pregnant women with preeclampsia have found gut microbiota dysbiosis (imbalance in gut microbiota composition) and increased plasma levels of lipopolysaccharide and trimethylamine N-oxide.
Recent evidence indicates that preeclampsia onset is associated with reduced bacterial diversity in gut microbiota. Specifically, the changes in gut microbiota include a depletion in beneficial bacteria and an enrichment in opportunistic bacteria.
Some mechanistic studies have pointed out that gut microbiota dysbiosis induces immune imbalance and intestinal barrier disruption in pregnant women, leading to the translocation of bacteria to the intrauterine cavity, placental inflammation, and poor placentation. All these factors collectively contribute to the development of preeclampsia.
Infant health impact of altered gut microbiota
Alteration in maternal gut microbiota has been found to affect the fetus's neurodevelopment via signaling microbially modulated metabolites to neurons in the developing brain. These changes can have long-term effects on an infant's behaviors.
Maternal microbiota-derived metabolites such as short-chain fatty acids are known to shape the metabolic system of infants. Some evidence has also indicated that maternal gut microbiota influences an infant's susceptibility to allergic diseases.