SERIAL HEMATOLOGIC CHANGES AND PREGNANCY OUTCOME

Objective: To reevaluate the concept that poor maternal hematologic ch anges relate to increased placental protein hormones, increased birth weight, and placenta to birth weight ratio. Methods: Sixty-nine normal women were studied prospectively. On several occasions, pre-pregnancy , during pregnancy, and post-delivery, plasma volume was measured toge ther with maternal hematologic indices and placental protein hormone l evels. Birth weight and placental weight were measured at delivery. Re sults: The decrements in hemoglobin concentration and hematocrit were apparent by 7 weeks' gestation. By 12 weeks, these progressive changes resulted mostly from the increase in plasma volume, and both hemoglob in concentration and hematocrit continued to decrease until near term. Increments in red cell and hemoglobin mass were maximal at 12-28 week s of pregnancy. Concentrations of the placental hormones hCG and human placental lactogen at 12 weeks showed a lack of correlation with hemo globin concentration or any other hematologic index. The correlations of birth weight with hemoglobin concentration and hematocrit at 36 wee ks were not significant when we controlled for the effect of plasma vo lume. Neither hemoglobin mass at 36 weeks nor the change in hemoglobin concentration, hematocrit, and mean cell volume from the pre-pregnanc y value to that at 36 weeks were significantly related to birth weight , placental weight, or the placenta to birth weight ratio. Conclusion: Low hemoglobin in late pregnancy reflects plasma volume changes, rath er than poor maternal nutrition or adaptation, and is not linked to di scordant placenta to birth weight ratio.