Anemia during pregnancy and birth outcome: A meta-analysis

To determine the relationship between maternal anemia [hemoglobin (Hgb) < 1 0-11 g/dL] and various birth outcomes, a meta-analysis was conducted based on published literature identified by MEDLINE and manual search from 1966 t hrough 1999. Odds ratios (OR) from selected studies were pooled according t o the gestational age at anemia diagnosis. The meta-analysis shows that mat ernal anemia during early pregnancy was associated with slightly increased preterm birth [pooled adjusted OR (aOR): 1.32, 95% confidence interval (CI) : 1.01-1.74], and nonstatistically significant increased low birth weight [ pooled aOR: 1.39 (0,70-2.74)], and was not associated with fetal growth res triction [pooled aOR: 1.01 (0.73_1.38)]. However, there was a nonstatistica lly significant inverse relationship between anemia during late pregnancy a nd preterm birth [pooled aOR: 0.92 (0.54-1.84)] and low birth weight [poole d aOR: 0.80 (0,64-1.00)]. Anemia was not statistically significantly associ ated with hypertensive disorders of pregnancy regardless of stage of pregna ncy [pooled OR: 0.80 (0,53-1.20)]. The relationship between anemia and peri natal mortality was inconclusive. A few studies indicated that severe mater nal anemia (Hgb < 8-8.5 g/dL) was associated with increased risk of poor ou tcomes. We conclude that early pregnancy anemia is associated with slightly increased risk of preterm birth. The trend toward an inverse association o f anemia determined during late pregnancy with preterm birth and low birth weight may reflect the benefit of plasma volume expansion.