Table 1.

Number of paired mother–infants from included studies

References	Country	No. of paired mothers and infants	No. of maternal samples	No. of infant samples	Mean inital paired reads (million) 95% confidence interval (95% CI)
Bäckhed et al.9	Sweden	98	98	294	39.9, 95% CI = [39.1; 40.7]
Chu et al.16	United States	10	15	12	28.0, 95% CI = [19.9; 36.0]
Asnicar et al.15	Italy	5	8	8	27.8, 95% CI = [23.1; 32.6]
Ferretti et al.17	Italy	21	21	81	35.5, 95% CI = [26.9; 44.0]
Pärnänen et al.18	Finland	16	32	32	12.5, 95% CI = [11.7; 13.2]
Yassour et al.8	Finland	38	106	152	33.2, 95% CI = [31.4; 34.9]
Wampach et al.20	Luxembourg	13 (one twin birth)	13	35	32.7, 95% CI = [27.7; 37.7]
Shao et al.19	United Kingdom	175 (three twin births)	175	410	19.9, 95% CI = [19.4; 20.4]