Background: In most sub-Sahara African countries, herbal medicines are widely used during pregnancy and labour for various motives despite their unclear pharmacology and potential toxicity. Considering the United Nations Sustainable Development Goal (SDG) 3, exposure to herbs during pregnancy should be restricted in order to safeguard the health of mothers and newborns. This study aimed to assess the proportion of mothers using herbal medicines during pregnancy and delivery and to determine factors associated with the practice.Methods: This cross-sectional quantitative study gathered information from 340 mothers who delivered a live baby in the preceding two years. Using a two-stage-sampling technique, we selected and interviewed mothers attending reproductive, maternal and child health clinics in Tabora, in central Tanzania. We compared proportions using chi-square test and performed a Poisson regression analysis to determine independent correlates of herbal use.Results: Over 60% of mothers in Tabora used herbal medicines during pregnancy and delivery. Major reasons for use were shortening of labour duration, 81 (38.9%) and reducing labour pain, 58 (27.9%). Independent factors of herbal use were distance to the nearest health facility, adjusted prevalence ratio (aPR = 1.12, 95%CI = 1.00,1.25), perception of herbs as safe, (aPR = 1.16, 95%CI = 1.05,1.29) and health care providers’ stance on the use of herbs, (aPR = 1.14, 95%CI = 1.04,1.25).Conclusions: Use of herbal medicines during pregnancy and delivery in Tanzania is high. This calls for comprehensive investigations on the effects of herbs used during pregnancy and delivery as a step towards understanding contributions of forgotten exposures en route for achieving SDG 3. Additionally, health care providers ought to include health education messages during antenatal visits on the undesirable effects of using herbs.