BACKGROUND: Dental caries is one of the most common chronic diseases of childhood and is associated with adverse health and economic consequences for infants and their families. Socioeconomically disadvantaged children have a higher risk of early childhood caries (ECC). OBJECTIVES: To assess the effects of interventions with pregnant women, new mothers or other primary caregivers of infants in the first year of life, for preventing ECC (from birth to six years of age). SEARCH METHODS: Cochrane Oral Health's Information Specialist searched the following databases: Cochrane Oral Health's Trials Register (to 14 January 2019), Cochrane Pregnancy and Childbirth Group's Trials Register (to 22 January 2019), Cochrane Central Register of Controlled Trials (CENTRAL) (Cochrane Register of Studies, to 14 January 2019), MEDLINE Ovid (1946 to 14 January 2019), Embase Ovid (1980 to 14 January 2019) and CINAHL EBSCO (1937 to 14 January 2019). The US National Institutes of Health Trials Registry (ClinicalTrials.gov) and World Health Organization International Clinical Trials Registry Platform were searched for ongoing trials. No restrictions were placed on language or publication status. SELECTION CRITERIA: Randomised controlled trials (RCTs) comparing one or more interventions with pregnant women, mothers, or other caregivers of infants in the first year of life (intervention types included clinical, oral health education/promotion such as hygiene education, breastfeeding and other dietary advice, and policy or health service), versus standard care or placebo or another intervention. For inclusion, trials had to report at least one caries outcome. DATA COLLECTION AND ANALYSIS: Two review authors independently assessed trial eligibility, extracted data, assessed risk of bias, and assessed certainty of evidence using the GRADE approach. MAIN RESULTS: We included 17 RCTs (4 cluster-randomised), involving 23,732 caregivers (mainly mothers) and their children. Eleven RCTs assessed four oral health education/promotion interventions against standard care: child diet advice, child diet and feeding practice advice, breastfeeding promotion and support, and oral hygiene with child diet and feeding practice advice. Six trials assessed clinical interventions in mother's dentition, four trials chlorhexidine (CHX, a commonly prescribed antiseptic agent) or iodine-NaF application and prophylaxis versus placebo, and two trials xylitol against CHX or CHX + xylitol. At most, three trials (maximum of 1148 children and 130 mothers) contributed data to any comparison. For many trials, risk of bias was judged unclear due to lack of methodological details reported, and there was high risk of attrition bias in some trials. None of the included trials indicated receiving funding that is likely to have influenced their results. The trials were performed in high-, middle- and low-income countries. In nine trials, participants were socioeconomically disadvantaged. For child diet and feeding practice advice versus standard care, we observed a probable 15 per cent reduced risk of caries presence in primary teeth with the intervention (RR 0.85, 95% CI 0.75 to 0.97; 3 trials; 782 participants; moderate-certainty evidence), and there may be a lower mean dmfs (decayed, missing, filled primary surfaces) score (MD -0.29, 95% CI -0.58 to 0; 2 trials; 757 participants; low-certainty evidence); however, we are uncertain regarding the difference between the groups in mean dmft (decayed, missing, filled teeth) score (MD -0.90, 95% CI -1.85 to 0.05; 1 trial; 340 participants; very low-certainty evidence). For breastfeeding promotion and support versus standard care, we observed that there may be little or no a difference between groups in the risk of caries presence in primary teeth (RR 0.96, 95% CI 0.89 to 1.03; 2 trials; 1148 participants; low-certainty evidence), or mean dmft score (MD -0.12, 95% CI -0.59 to 0.36; 2 trials; 652 participants; low-certainty evidence). Dmfs was not reported for this comparison. We are uncertain whether child diet advice only compared with standard care reduces risk of caries presence in primary teeth (RR 1.08, 95% CI 0.34 to 3.37; 1 trial; 148 participants; very low-certainty evidence). Dmfs and dmft were not reported for this comparison. For oral hygiene, child diet and feeding practice advice versus standard care, we observed little or no reduced risk of caries presence in primary teeth (RR 0.91, 95% CI 0.75 to 1.10; 2 trials; 365 participants; low-certainty evidence), and are uncertain regarding difference between the groups in mean dmfs score (MD -0.99, 95% CI -2.45 to 0.47; 1 trial; 187 participants; very low-certainty evidence) and dmft score (MD -0.30, 95% CI -0.96 to 0.36; 1 trial; 187 participants; very low-certainty evidence). We observed there may be little or no difference in risk of caries presence in primary teeth between antimicrobial and placebo treatment in mother's dentition (RR 0.97, 95% CI 0.80 to 1.19; 3 trials; 479 participants; very low-certainty evidence). No trials assessing this comparison reported dmfs or dmft. For xylitol compared with CHX antimicrobial treatment, we observed there may be a lower mean dmft score with xylitol (MD -2.39; 95% CI -4.10 to -0.68; 1 trial, 113 participants; low-certainty evidence); however, we are uncertain regarding the difference between groups in caries presence in primary teeth (RR 0.62, 95% CI 0.27 to 1.39; 1 trial, 96 participants; very low-certainty evidence). Neither trial evaluating this comparison reported dmfs. No trials assessed a health policy or service intervention. AUTHORS' CONCLUSIONS: Moderate-certainty evidence suggests that providing advice on diet and feeding to pregnant women, mothers or other caregivers with children up to the age of one year probably leads to a slightly reduced risk of early childhood caries (ECC). The remaining evidence is low to very low certainty and is insufficient for determining which, if any, other interventions types and features may be effective for preventing ECC. Large, high-quality RCTs of oral health education/promotion, clinical, and policy and service access interventions, are warranted to determine effects and relative effects of different interventions and inform practice. We have identified 12 studies currently in progress. Those designing future studies should describe the intervention components, setting and participants, consider if and how effects are modified by intervention features and participant characteristics, and adopt a consistent approach to measuring and reporting ECC.