Plasma beta-endorphin-like immunoreactivity, self reported pain perception and anxiety levels in women during pregnancy and labor.

Plasma Beta-endorphin (B-END) immunoreactivity was measured in 19 men, 16 women at midcycle, and ten pregnant women at various points in their pregnancies. There is a significant difference between the levels measured in males and females (t = 3.74, df = 31, p = .0007). Pregnant women demonstrated a steady increase in plasma Beta-End-like immunoreactivity between second and third trimester and through labor. The levels dropped rapidly postpartum. The material being measured is predominantly B-end-sized. Psychological studies indicate that these changes are not strongly correlated with pain perception or self-reported anxiety levels.