What do systematic reviews say?

Probiotics administered to pregnant women at risk of preterm birth vs placebo or no intervention

Probiotics administered to pregnant women at risk of preterm birth showed no clear difference in preterm birth < 37 weeks' gestation compared with placebo or no intervention (low certainty).

• Maternal probiotic supplementation for prevention of morbidity and mortality in preterm infants 2018 · Cochrane Headline outcomes only
  RR 0.92 [0.32, 2.67]
  4 studies · 518 participants
  Low

Probiotics administered to pregnant women at risk of preterm birth vs placebo or no intervention

• Maternal probiotic supplementation for prevention of morbidity and mortality in preterm infants 2018 · Cochrane Headline outcomes only
  no estimate extracted
  2 studies · 287 participants
  Very low