The relation between serum levels of pregnancy-specific beta 1-glycoprotein (SP1) and actual fetal and placental weights was studied in 100 full-term pregnant women. This was compared with fetal weight determination by ultrasound. SP1 levels significantly correlated with fetal and placental weights. Its determination was found to be comparable to ultrasonography in placental fetal weight assessment, especially at the extremes of fetal weight (macrosomia and small for gestational age) where special obstetric management is warranted.