Background The aim of this study was to determine the relationship between maternal anemia during pregnancy and pregnancy outcomes. Materials and Methods This systematic review was conducted in domestic (Sid, Iran.doc, Iran medex and Magiran) and international (PubMed, Science Direct, Cochrane, Medline, Web of Science, Scopus, Springer, Embase, Google scholar) databases from January 1, 1990 to April 10, 2016 with using standard key words "Pregnancy", "Pregnant women", "Hemoglobin/ haemoglobin", "Anemia/ anaemia", and "Pregnancy outcome". Relative risks (RR) and confidence intervals were extracted from each study. Results Overall 30 studies with a total sample size of 1,194,746 were entered into the final meta-analysis. Maternal anemia in the first trimester showed a significant relationship with low birth weight (RR: 1.28, 95% CI, 1.10 - 1.50, P0.05) and pre-term birth (RR: 1.55, 95% CI, 0.83 - 2.88, P>0.05). Conclusion Maternal anemia during pregnancy in the first trimester in particular can be considered as a risk factor for pregnancy outcomes and must be treated as an advance
