The gut microbiome in early pregnancy is associated with the severity of nausea and vomiting: a nested case‒control study.

Approximately 70% of all pregnancies are affected by nausea and vomiting (NVP), yet the mechanisms controlling this phenomenon are not well known. Pregnancy hormones explain a large part of this effect, mostly through human chorionic gonadotropin and fetal production of GDF15, a hormone active in the brain stem. Still, there is a wide variation in the severity of symptoms, ranging from no nausea to severe vomiting requiring hospitalization (hyperemesis gravidarum). Here, we present a nested case‒control study within the large SweMaMi cohort, wherein 337 participants with severe NVP in early pregnancy were matched 1-to-1 with moderate and mild NVP, respectively. Subjects with more severe nausea had lower richness and diversity in their fecal microbiomes. Several taxa were significantly associated with NVP score, where the most extreme are a negative correlation with Lactobacillaceae and positive correlations with Bifidobacterium dentium and Puniceicoccaceae. Finally, higher NVP score was associated with a higher abundance of bacteria encoding for the neuroactive pathways of glutamine degradation, inositol synthesis, and lactate production. In conclusion, the gut microbiota was strongly associated with NVP. Further studies with direct interventions capable of restoring the early-pregnancy gut microbiome could open up new approaches for dealing with the most common symptom of early pregnancy.