High and low hemoglobin levels during pregnancy: differential risks for preterm birth and small for gestational age

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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.

Conclusion: 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.

Section snippets

Materials and methods

Data for this study were obtained from publicly funded maternal child health program clinic records submitted to the CDC Pregnancy Nutrition Surveillance System between 1990 and 1993. Ninety-six percent of the records were from women attending the Special Supplemental Nutrition Program for Women, Infants, and Children. We included all surveillance records on singleton pregnant women from 11 states in the United States who entered the maternal child health program between 1 and 36 weeks’

Results

Table 3 shows maternal and infant characteristics by trimester of entry into the maternal-child health program, the trimester during which maternal hemoglobin level was measured. Because of the large sample size in each group, even small differences were statistically significant. Thus, the magnitude of the relative differences rather than their statistical significance was examined. Relative differences of more than 25% were considered noteworthy.

Women who entered the maternal-child health

Discussion

We found that maternal anemia during pregnancy was associated with preterm birth but not with delivery of an SGA infant. Moreover, high maternal hemoglobin level was associated with SGA but not with preterm birth. We observed the strongest increased risk of preterm birth among women with more severe anemia (hemoglobin Z score less than −3.0), which corresponds to an approximate hemoglobin level less than 90 g/L to 100 g/L, depending on week of gestation (Table 2). The strongest risk of SGA was

References (24)

  • Screening for iron deficiency anemia-including iron prophylaxis

  • S.M Garn et al.

    Maternal hematological levels and pregnancy outcomes, Semin Perinatol

    (1981)
  • Cited by (0)

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