Parity influences on the infant gut microbiome development: a longitudinal cohort study.

Parity, the number of pregnancies carried beyond 20 weeks, influences the maternal gut microbiome. However, whether parity modulates the infant microbiome longitudinally remains underexplored. To address this, 746 infants in a longitudinal cohort study were assessed. Serial infant stool samples collected at 2, 6, 12, and 24 months underwent 16S ribosomal RNA gene sequencing. Mothers were stratified by parity: 1 = 32.6%, 2 = 42.0%, 3 = 18.6%, 4, 5, 6 or 7 = 6.8%. Although no differences in alpha diversity were found with parity, significant differences were found in microbiome composition (beta diversity, Bray-Curtis) by parity at each time point through the first year of life ( < 0.001). Delivery mode (vaginal delivery (VD) = 60.5%, Cesarean section (CS) = 39.5%) was a significant contributor to infant microbiome composition at 2 months ( = 0.002). In VD infants, parity-related differences in microbiota composition were evident up to 6 months ( ≤ 0.002), however in CS delivered infants, early life parity-related differences were absent. In conclusion, our brief report showed a significant effect of parity on early infant gut microbiome composition. However, the effect of parity diminished with CS delivery, which we hypothesize is due to decreased mother-to-infant microbiome transfer with CS. These results demonstrate the necessity of including parity in longitudinal infant microbiome analyses.