Facts and artifacts about anemia and preterm delivery

Area of Science:

• Obstetrics and Gynecology
• Maternal-Fetal Medicine
• Hematology

Background:

• Anemia is a common condition in pregnancy.
• Its role in preterm birth, particularly in diverse populations, requires further investigation.

Purpose of the Study:

• To prospectively examine the association between anemia and preterm birth.
• To investigate if anemia contributes to the higher preterm birth rates observed in Black women.

Main Methods:

• A prospective study of 35,423 pregnancies.
• Comparison of preterm birth incidence between anemic and non-anemic women weekly during the third trimester.
• Analysis of hematocrit changes from 25 weeks gestation to term in relation to infant birth weight and maternal race.

Main Results:

• A weak association was found between anemia early in the third trimester and preterm delivery.
• Anemia early in gestation did not explain the increased preterm birth rate among Black women.
• Anemia after 30 weeks' gestation was not linked to preterm birth.
• Hematocrit levels increased from 25 weeks to term in both Black and White women delivering term infants.
• The association between anemia and preterm birth appeared strongest at 28 weeks and diminished as term approached.
• Comparing hematocrit levels between women in preterm and term labor created a spurious dose-response effect.

Conclusions:

• Anemia is not a significant factor in the development of preterm birth.
• Methodological issues, such as comparing hematocrits in women in labor, can bias results.
• Further research should account for these biases when assessing anemia's impact on pregnancy outcomes.