Definition 2: <6 month vs. >=6 month
Operating surgery when patient more than 6 months old did not significantly decrease the operative time (P=0.95), with high heterogeneity (I2=89.5%). The publication bias was assessed and not detected. When we performed he subgroup analysis, we found that in groups with sample size >=200, patient younger than 6 months old could decrease the operative time (p=0.004), with low heterogeneity (I2=0%).