Introduction
Microbiome refers to a totality of microorganisms, their genetic material, and their interactions in a defined environment. It exists naturally and can be seen in water, soil, and humans. A human microbiome refers to the total collection of microbes (viruses, fungi, bacteria, etc.) and their genetic material in the human body in a specific habitat (a habitat can be the whole body itself or a specific region). The largest habitat with the most complex microbes is the gastrointestinal system. Though bacteria cause infection, they are also beneficial to the human host. Studies show that the microbiome is important in pregnancy and preterm delivery. The variability between beneficial and harmful bacteria results in disease or illness.
What Is the Role of the Gut Microbiome in Gestational Complications?
Changes in the composition of the gut microbiome affect the host’s metabolism, digestion, immunity, and neurodevelopment. These changes can affect different parts of the maternal body, like the intestine, oral cavity, breast milk, and vagina.
1. Gestational Diabetes Mellitus:
When considering diabetic pregnant women, more than 80 percent have gestational diabetes. The glucose metabolism usually returns to normal after childbirth, but women have an increased risk of developing diabetes mellitus in the future. Studies showed that pregnant women with gestational diabetes were found to have an abundance of certain microbes like Actinobacteria, Firmicutes, Rothia, etc. Such gestational patients were also found to have changes in placental microbiomes compared to those with normal blood sugar levels.
2. Preeclampsia:
Preeclampsia refers to elevated blood pressure and proteins in the urine after five months of pregnancy. Studies suggest that the gut microbiome is linked to the cause of preeclampsia.
Mainly, studies suggest:
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The gut microbiome plays an important role in preeclampsia in pregnant women.
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An imbalance in the placental microbiome may be related to preeclampsia.
3. Obesity:
When a woman gains weight exceeding the normal range weight gain expected in a pregnant woman, the condition is referred to as gestational diabetes. Gestational obesity can adversely affect both the fetus and the mother. Hormonal imbalances are mostly responsible for this condition. Some studies have found an association between gestational obesity and high levels of Bacteroides species in the intestine.
4. Digestive Tract Diseases:
Studies have shown a relationship between the gut microbiome and fetal and maternal digestive tract diseases.
5. Autoimmune Diseases:
Autoimmune diseases refer to the condition in which the body’s immune system attacks the autoantigen, leading to tissue damage. Autoimmune diseases mostly affect women when compared to men. Studies suggest a link between the gut microbiome and various autoimmune disorders like rheumatoid arthritis and SLE (Systemic lupus erythematosus). Studies suggest that an imbalance in the gut microbiome during pregnancy leads to changes in autoimmune responses.
What Are the Effects of the Maternal Microbiome on the Fetus?
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Effect on Fetal Immune System:
The maternal microbiome plays a vital role in fetal health too. The development of the microbiome in the fetus is linked to the existing microbiome in the mother. It can be transmitted through vertical transmission from the mother to the fetus. The transmission mostly occurs during delivery and postpartum, when the infant is exposed to the mother’s vagina, feces, and skin. Studies show that the maternal microbiome plays a significant role in the fetus's immune system.
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Effect on Fetal Neurodevelopment:
Some symbiotic microbiomes in humans are linked to the host’s nerve and brain development. Changes in the host microbiome have been linked to neurological disorders like stress, anxiety, depression, and autism.
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Neonatal Gastrointestinal Disease:
All know that the gut plays an important role in digestion and absorption; it also plays a role in immunity. Prenatal infants are found to have abnormal colonization (only fewer bacterial colonization is seen) and are exposed to highly infective institutional microbes as they are born via C-section. The intestinal microbiome in premature infants is linked to the pathogenesis of inflammatory gastrointestinal disorders like necrotizing enterocolitis (NEC).
What Is the Role Between Microbiome and Preterm Birth?
Preterm delivery is one of the leading causes of neonatal morbidity and mortality globally. Though there are several causes of preterm birth, studies show that microbes causing intra-uterine infection play a significant role in preterm birth.
The potential sites for infection within the uterus are:
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Within the fetal membrane.
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Within the placenta.
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Within the amniotic fluid.
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Umbilical cord.
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Choriodecidual space (space between the fetal membrane and maternal tissue).
In most cases, the infections are subclinical, with few symptoms or signs. Studies found that the amniotic fluid of patients who underwent spontaneous labor (those with intact membranes) harbored a more complex variety of microbes than was expected.
How Does the Type of Delivery Affect the Fetal Microbiome?
The fetus is believed to develop in a sterile uterine environment, and the initial microbial exposure occurs at birth. If the child is delivered via vaginal delivery, the fetal bacterial exposure will represent microorganisms present in the maternal vagina. If the child is delivered via C-section, the fetal bacterial exposure will represent microorganisms in the maternal skin.
The direct vertical transmission of the vaginal microbiome to the fetus during delivery is an important defense mechanism. Studies show that about 60 to 82 % of all MRSA (methicillin-resistant Staphylococcus aureus) infections are seen in infants born via C-section.
Conclusion
The variability of the microbiome is what results in disease or health. Studies show a significant link between the microbiome and perinatal health. The variation in the gut microbiome has been linked to many gestational complications. Studies show that the maternal microbiome affects fetal neurodevelopment and immunity. Microbes that cause intra-uterine infections are also linked to preterm delivery, an important cause of infant mortality. The type of delivery (vaginal or C-section) affects the fetal microbiome, as direct vertical transmission of the microbiome from mother to baby occurs.
