Introduction: Effects of daily iron supplementation in iron replete pregnancy are unclear. This systematic review aimed to assess benefits and harms of oral iron supplements in pregnant women without anemia and iron deficiency. Material and methods: We predefined and registered a protocol in PROSPERO (CRD42020186210) and performed the review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology. We searched for randomized clinical trials (RCTs) and observational studies comparing daily oral iron supplementation with no iron supplements in non-anemic iron replete pregnant women. Searches were conducted in MEDLINE (by PubMed), EMBASE (by OVID), Cochrane Library, and ClinicalTrials.gov from inception to September 2022 without language restrictions. Two authors independently screened records, extracted data, and assessed risk of bias using the revised Cochrane risk of bias tool (RoB2). One author read full-texts, assessed certainty of evidence by GRADE and conducted meta-analyses using a random-effects model. Primary outcomes included iron deficiency anemia, iron deficiency, hemoglobin >130 g/L, elevated iron status, small for gestational age newborns, low birthweight newborns, preterm birth, and congenital anomalies. Results: Eight RCTs (2822 women) but no observational studies were eligible for inclusion. Daily oral iron supplementation in pregnancy probably reduces iron deficiency anemia at term (risk ratio [RR]: 0.51, 95% confidence interval [CI]: 0.38–0.70; 4 RCTs, 1670 women; I² = 13%; moderate-certainty evidence) and the incidence of low birthweight babies (RR: 0.30, 95% CI: 0.13–0.68; 2 RCTs, 361 infants; I² = 0%; moderate-certainty evidence). In addition, it may reduce iron deficiency at term (RR: 0.74, 95% CI: 0.60–0.92; 4 RCTs, 1663 women; I² = 58%; low-certainty evidence) and the incidence of small for gestational age babies (RR: 0.39, 95% CI: 0.17–0.86; 1 RCT, 213 infants; I² not estimable; low-certainty evidence). Conclusions: Daily iron supplementation in iron replete non-anemic pregnant women probably reduces the risk of maternal iron deficiency anemia at term and low birthweight.