For very low birth weight (VLBW) premature infants, there is even more evidence that probiotics are effective (The Journal of Pediatrics Volume 165, Issue 2 , Pages 285-289.e1, August 2014 -thanks to Kipp Ellsworth for abstract link).

Abstract (goo.gl/ba1dlU ):

Study design

Within the observational period (September 1, 2010, until December 31, 2012, n = 5351 infants) study centers were categorized into 3 groups based on their choice of Lactobacillus acidophilus/Bifidobacterium infantis use: (1) no prophylactic use (12 centers); (2 a/b) change of strategy nonuser to user during observational period (13 centers); and (3) use before start of observation (21 centers). 

Results

The use of probiotics was associated with a reduced risk for necrotizing enterocolitis surgery (group 1 vs group 3: 4.2 vs 2.6%,P = .028; change of strategy: 6.2 vs 4.0%, P < .001), any abdominal surgery, and hospital mortality. Infants treated with probiotics had improved weight gain/day, and probiotics had no effect on the risk of blood-culture confirmed sepsis. In a multivariable logistic regression analysis, probiotics were protective for necrotizing enterocolitis surgery (OR 0.58, 95% CI 0.37-0.91; P = .017), any abdominal surgery (OR 0.7, 95% CI 0.51-0.95; P = .02), and the combined outcome abdominal surgery and/or death (OR 0.43; 95% CI 0.33-0.56; P < .001).