title: High and low hemoglobin levels during pregnancy: differential risks for preterm birth and small for gestational age.
abstract: OBJECTIVE
  To examine the association of maternal hemoglobin during pregnancy with preterm birth and small for gestational age (SGA).
  
  
  METHODS
  We performed a retrospective cohort analysis of hemoglobin and birth outcome among 173,031 pregnant women who attended publicly funded health programs in ten states and delivered a liveborn infant at 26-42 weeks' gestation. We defined preterm as less than 37 weeks' gestation and SGA as less than the tenth percentile of a US fetal growth reference.
  
  
  RESULTS
  Risk of preterm birth was increased in women with low hemoglobin level in the first and second trimester. The odds ratio (OR) for preterm birth with moderate-to-severe anemia during the first trimester (more than three standard deviations [SD] below reference median hemoglobin, equivalent to less than 95 g/L at 12 weeks' gestation) was 1.68 (95% confidence interval [CI] 1.29, 2. 21). Anemia was not associated with SGA. High hemoglobin level during the first and second trimester was associated with SGA but not preterm birth. The ORs for SGA in women with very high hemoglobin level during the first and second trimester (more than three SDs above reference median hemoglobin, equivalent to greater than 149 g/L at 12 weeks' gestation and greater than 144 g/L at 18 weeks') were 1.27 (95% CI 1.02, 1.58) and 1.79 (95% CI 1.49, 2.15), respectively.
  
  
  CONCLUSIONS
  These data highlight the importance of considering anemia and high hemoglobin level as indicators for adverse pregnancy outcome. An elevated hemoglobin level (greater than 144 g/L) is an indicator for possible pregnancy complications associated with poor plasma volume expansion, and should not be mistaken for good iron status.
authors.affiliation: Division of Nutrition and Physical Activity and the Division of Reproductive Health, Centers for Disease Control and Prevention, Atlanta, Georgia, USA. kxs5@cc.gov
authors.forename: K S
authors.initials: KS
authors.lastname: Scanlon
authors.forename: R
authors.initials: R
authors.lastname: Yip
authors.forename: L A
authors.initials: LA
authors.lastname: Schieve
authors.forename: M E
authors.initials: ME
authors.lastname: Cogswell
mesh_terms: D000293:Adolescent; D000328:Adult; D000740:Anemia / Q000150:complications*; D002648:Child; D002681:China / Q000453:epidemiology; D015331:Cohort Studies; D005260:Female; D005317:Fetal Growth Retardation / Q000453:epidemiology* / Q000209:etiology; D005865:Gestational Age; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D007231:Infant, Newborn; D007752:Obstetric Labor, Premature / Q000453:epidemiology* / Q000209:etiology; D010953:Plasma Volume; D011247:Pregnancy; D011250:Pregnancy Complications, Hematologic; D011256:Pregnancy Outcome; D011264:Pregnancy Trimesters; D012189:Retrospective Studies; D012307:Risk Factors
chemical_list: D006454:Hemoglobins