Effect of smoking on maternal blood SP1 levels in late pregnancy.

Maternal blood levels of pregnancy-specific beta 1-glycoprotein (SP1) were measured in 1669 samples from 1078 patients at 31 to 40 weeks' gestation. Mothers who smoked throughout pregnancy showed a general reduction in infant birth weight and blood SP1 levels. Further analysis of these findings showed that SP1 levels were directly related to fetal weight, and suggested that smoking affects fetus and placenta as a single unit.