The Influence of Maternal Obesity on Microbial Function and Impaired Glucose Tolerance during Pregnancy

Background: Recent technological advances in next-generation genomic sequencing and bioinformatics have allowed researchers to examine the biological underpinnings of obesity through the lens of the human microbiome; however, the state of the science during pregnancy has yet to identify exact mechanisms. With obesity being one of the most common complications in pregnancy, further work is necessary to establish the downstream maternal and child outcomes of increased body mass index (BMI) and alterations to the maternal gastrointestinal microbiome. The purpose of this dissertation was to examine the influence of maternal obesity on microbial composition and function, its relationship with impaired glucose tolerance in the late second trimester, and to explore the association between the microbiota and neonatal birth weight adjusted for gestational age at delivery.

Design: Retrospective, cross-sectional study of maternal gastrointestinal microbiome biospecimens from 109 participants enrolled in the Obstetrics and Neonatal Outcomes Study.

Results: Our results show that there are differences in composition and function between maternal pre-gravid BMI groups in the late second trimester of pregnancy. Women who enter into pregnancy with an overweight or obese BMI have a significantly lower alpha diversity of microbes present in the gut at a critical time period of blood glucose regulation as the body’s requirements for insulin drastically increase to support fetal growth. While there were no significant differences in mean blood glucose value on the glucose challenge test between BMI groups, there are microbial factors that, through the moderation of glucose tolerance, have a significant effect on neonatal birth weight adjusted for gestational age.

Conclusion: While women with pre-gravid obesity do have significant differences in their microbiota in the late second trimester, we believe that the maternal microbiota attempts to regulate both the metabolic and immune systems to preserve the growth of the fetus. However, this compensation may not last and, instead, instantiate harm to her health in the long term. The findings from this study deepen our scientific understanding of the complexities of the maternal microbiome and its role in impaired glucose tolerance and adverse neonatal outcomes. Future research should focus on how the maternal microbial environment affects not only her child’s health but her health and wellbeing as shown highlighted during the vulnerability of pregnancy.