fig2

Figure 2. Overview of studies included in this review. On the X-axis, the sampling period is shown, expressed in weeks of PMA. (A) Subgroup A consists of studies where infants received 100% human milk (MOM/DHM); (B) Subgroup B consists of studies where infants received a combination of human milk (MOM/DHM) and PF. Note: To express the maturity stage of infants at the time of sample collection, we calculated PMA during sampling collection time points. For the start of the PMA range, we added the earliest time point of sample collection to the lowest mean or median gestational age from both groups (MOM and DHM). For the end of the PMA range, we added the latest time point of sample collection to the highest mean or median gestational age from both groups. For studies that stated sampling at the day of achieving full enteral feeding, but not explicitly mentioning at which day of life this was, we arbitrarily chose ten days of age as the mean age of achieving full enteral feeding in order to calculate the PMA during sample collection^[38]. N means number of stool samples collected at one or multiple time points. ^*N for all time points combined. Created with Biorender.com. PMA: Postmenstrual age; MOM: mother’s own milk; DHM: donor human milk; PF: preterm formula; GA: gestational age; DoL: day of life; WoL: week of life; FEFA: full enteral feeding achieved.