Aim of our study was to retrospectively evaluate whether the oral administration of L. crispatus (M247) could increase pregnancy and live birth rates in women undergoing assisted reproductive technology procedures. Enrolled women (N=160) were divided into two groups: treated (N=80) or untreated (N=80) with the probiotic strain. The odds ratio for a treated woman to get a positive pregnancy test (PPT) was 1.56. In women aged 30–40 years, M247 increased the probability of a PPT in correlation with the progressive rise in BMI, reaching 47% (35% in controls) with a BMI of 35 (odds ratio: 2.00). The CAID statistics showed that in a woman of the blastocyst subgroup, below 43 years, with a BMI over 18.6, treatment with M247 increased the chance of a PPT from 28.4% to 44.5% (odds ratio: 2.08; p<0.05). Considering live births, rate of probiotic group was 12.5% versus 7.5% (odds ratio=1.76). Considering only the blastocyst subgroup, the treatment increased the number of live births by 200% (odds ratio: 3.64; p=0.05). As confirmed also by statistical indices like NNT, NNH and LHH, the use of M247 demonstrated a risk-benefit ratio to the full advantage of the benefits.