Appropriate nutrition during pregnancy and the post-partum period is vital to both the parent and their offspring. Both under- and over-nourished status may have important microbial implications on the parental and infant gut microbiomes. Alterations to the microbiome can have implications for a person’s risk of obesity and metabolic diseases. In this review, we examine alterations in the parental gut, vaginal, placental, and milk microbiomes in the context of pre-pregnancy BMI, gestational weight gain, body composition, gestational diabetes, and parental diet. We also investigate how the infant gut microbiome may be altered by these different parameters. Many of the microbial changes seen in under- and over-nourished states in birthing parents may result in long-term implications to the health of offspring. Differences in diet appear to be a major driver of the parental, and subsequently milk and offspring microbiomes. Further prospective longitudinal cohort studies are needed examining nutrition and the microbiome to better understand its implications. Additionally, trials involving dietary interventions in child-bearing age adults should be explored to improve the parent and child’s risks for metabolic diseases.