title: Hemoglobin concentration and pregnancy outcomes: a systematic review and meta-analysis.
abstract: OBJECTIVE
  To conduct a systematic review and meta-analysis of hemoglobin effect on the pregnancy outcomes.
  
  
  METHODS
  We searched MEDLINE and SCOPUS from January 1, 1990 to April 10, 2011. Observational studies addressing association between hemoglobin and adverse pregnancy outcomes were selected. Two reviewers independently extracted data. A mixed logistic regression was applied to assess the effects of hemoglobin on preterm birth, low birth weight, and small for gestational age.
  
  
  RESULTS
  Seventeen studies were included in poolings. Hemoglobin below 11 g/dL was, respectively, 1.10 (95% CI: 1.02-1.19), 1.17 (95% CI: 1.03-1.32), and 1.14 (95% CI: 1.05-1.24) times higher risk of preterm birth, low birth weight, and small for gestational age than normal hemoglobin in the first trimester. In the third trimester, hemoglobin below 11 g/dL was 1.30 (95% CI: 1.08-1.58) times higher risk of low birth weight. Hemoglobin above 14 g/dL in third trimester decreased the risk of preterm term with ORs of 0.50 (95% CI: 0.26-0.97), but it might be affected by publication bias.
  
  
  CONCLUSIONS
  Our review suggests that hemoglobin below 11 g/dl increases the risk of preterm birth, low birth weight, and small gestational age in the first trimester and the risk of low birth weight in the third trimester.
authors.affiliation: Section for Clinical Epidemiology and Biostatistics, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Rama VI Road, Rachatevi, Bangkok 10400, Thailand.
authors.forename: Bunyarit
authors.initials: B
authors.lastname: Sukrat
authors.forename: Chumpon
authors.initials: C
authors.lastname: Wilasrusmee
authors.forename: Boonying
authors.initials: B
authors.lastname: Siribumrungwong
authors.forename: Mark
authors.initials: M
authors.lastname: McEvoy
authors.forename: Chusak
authors.initials: C
authors.lastname: Okascharoen
authors.forename: John
authors.initials: J
authors.lastname: Attia
authors.forename: Ammarin
authors.initials: A
authors.lastname: Thakkinstian
mesh_terms: D005260:Female; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D007230:Infant, Low Birth Weight / Q000097:blood; D007236:Infant, Small for Gestational Age / Q000097:blood; D011247:Pregnancy; D011256:Pregnancy Outcome; D011261:Pregnancy Trimester, First / Q000097:blood; D011263:Pregnancy Trimester, Third / Q000097:blood; D047928:Premature Birth / Q000097:blood
chemical_list: D006454:Hemoglobins