Major basic protein as a predictor of preterm labor: a preliminary report.

To determine the association between levels of major basic protein and onset of preterm labor, plasma levels of major basic protein were measured in 13 women from weeks 22 to 41 of gestation. Twelve of the 13 women studied experienced spontaneous onset of labor. All of these women demonstrated a late rise in serum levels of major basic protein characterized by an increase in concentration of 156% +/- 14%. A temporal association between a rise in concentrations of major basic protein and the onset of preterm labor, which was successfully treated with tocolytic agents, was observed in three patients. Increases in major basic protein began 3 to 4 weeks before delivery. The rise in levels of major basic protein was absent in one patient who was delivered of her infant at 30 weeks' gestation after induction of labor with oxytocin. Analysis of these data indicate that a protein marker is associated with the onset of human labor not only at term but also preterm.