This clinical practice guideline on the supply of the omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) in pregnant women for risk reduction of preterm birth (PTB) and early PTB was developed with support from several medical-scientific organizations, based on reviewing available strong evidence from randomized clinical trials and a formal consensus process. We conclude: Women of childbearing age should obtain a supply of at least 250 mg/d DHA plus EPA from diet or supplements, and in pregnancy an additional intake of ≥100-200 mg/d DHA. Pregnant women with a low DHA intake and/or low DHA blood levels have an increased risk of PTB and early PTB; they should receive a supply of about 600-1000 mg/day of DHA plus EPA, or DHA alone, which showed significant reduction of PTB and early PTB in randomized controlled trials. This additional supply should preferably begin in the second trimester of pregnancy (not later than about 20 weeks' gestation) and continue until about 37 weeks' gestation, or until childbirth if before 37 weeks' gestation. Identification of women with inadequate omega-3 supply is achievable by a set of standardized questions on intake. DHA measurement from blood is another option to identify women with low status, but further standardization of laboratory methods and appropriate cutoff values is needed. Information on how to achieve an appropriate intake of DHA or DHA + EPA for women of childbearing age and pregnant women should be provided to women and their partners.