The Effect of Probiotics on Health in Pregnancy and Infants: A Randomized, Double-Blind, Placebo-Controlled Trial

Background/Objectives: There is growing interest in the benefits of probiotic supplementation during pregnancy and lactation, but evidence supporting the beneficial effects for mother-infant dyads remains scarce. This study assessed the effects of probiotic supplementation on infection frequency and immunity in pregnant women and infants, and on microbiome establishment during the first month of life. Methods: At 28 weeks of gestation, 180 healthy pregnant women were randomized to receive either a placebo (n = 90) or a probiotic supplement (n = 90), Prenatis™, containing 5 billion CFU/day of Lacticaseibacillus rhamnosus Rosell^®-11 and Bifidobacterium bifidum HA-132. Results: There was a significantly lower number of women with one or more infections during the study in the probiotics group (8 vs. 18, p = 0.05) and a trend for a lower number of infections during pregnancy (primary outcome) in the probiotics group (p = 0.07). Regarding infants, a lower number of days with infections during the first month of life was observed in the probiotics group (4.7 days on average vs. 10.5 days, p = 0.03). The vaginal microbiota composition during pregnancy and after childbirth showed no significant differences between groups while the infants' gut microbiome demonstrated a significantly higher abundance/prevalence of beneficial taxa in the probiotics group. The benefits conferred by probiotics were especially notable when considering birth by C-section. Probiotics promoted the vertical transmission of beneficial species and the induction of a highly interconnected microbiota, structured around key species. Conclusions: Probiotic supplementation during the third trimester of pregnancy and lactation is a valid strategy for conferring benefits to mothers and infants.