Methodological quality and risk of bias
The quality of the cohort studies was characterized as good, as measured
by the Newcastle-Ottawa scale, with most studies scoring ≥ 7 out of 9
points (Table 1). The RCTs were assessed using the Cochrane
Collaboration risk of bias (RoB) tool (11). Although all included RCTs
conducted randomization, five of them did not adequately describe their
randomization methods. Only two studies used sequentially numbered
sealed opaque envelopes for allocation, 1 used a third party for
allocation, 1 used software-generated random number sequence for
allocation and the others never mentioned an allocation scheme. Eleven
studies had an unclear risk of bias due to performance and detection
bias. The infants and personnel could not be blinded due to the nature
of intervention and three studies were judged to have a high risk of
bias due to performance bias; however, the outcome assessor was blinded,
resulting in a low risk of bias due to detection bias (suppl. eFig. 1,
eFig. 2).