HEMOCONCENTRATION IN SMOKING MOTHERS IS ASSOCIATED WITH IMPAIRED FETAL GROWTH

Objective. To examine the effect of maternal smoking on the relationsh ip between maternal hemoglobin levels and pregnancy outcome. Design. A prospective study of healthy parous women from early pregnancy and of their infants. Setting. Three Scandinavian university hospitals cover ing all deliveries from well defined,geographical areas. Subjects. Smo king (669) and non-smoking (368) mothers, para 1 and 2 and with greate r than or equal to 37 weeks of gestational length. Main outcome measur es. Birth weight and placental weight. Ponderal Index and Placental In dex as measures of possible discordant fetal and placental growth. Res ults. In non-smoking mothers the hemoglobin levels in the three trimes ters had no relation to birth weight. In smoking mothers a significant ly lower birth weight was seen with a high hemoglobin level in the thi rd trimester, but hemoglobin levels in early or mid-pregnancy had no a ssociation to birth weight. Smoking mothers also had a significantly g reater fall in hemoglobin concentration from first to second and third trimester as compared to nonsmokers although ferritin levels were sim ilar in smokers and non-smokers, implying similar iron stores. The rat io of placental weight to the weight of the newborn was significantly higher in smokers, but no association was found to different hemoglobi n levels. Conclusions. Fetal growth impairment associated with materna l smoking is even more pronounced in smoking mothers with high hemoglo bin levels in late pregnancy. Smoking mothers were also found to have disproportional fetal/placental growth with relatively high placental weights. In non-smoking mothers hemoglobin levels had no relation to b irthweight.