Primary prostaglandins in amniotic fluid in pregnancy and spontaneous labor.

Primary prostaglandins have been measured by radioimmunoassay in the amniotic fluid of 80 patients. In late pregnancy, PGE2 was higher than PGF2alpha with an increase around 36 weeks (378 +/- 71 pg. per milliliter) without significant modification until term. PGF2alpha increased too, but only significantly at term. During spontaneous labor, PGE2 and PGF2alpha were higher than before the onset of labor. Through serial determinations in five patients, two steps can be distinguished: the first one with stable levels but large oscillations of PGE2 and PGF2alpha and the second one starting at a variable stage of cervical dilatation with inversion of PGE2/PGF2alpha ratio (less than 1 and followed by an increase of both compounds more pronounced for PGF2alpha. It appears that PGE2 is concerned with the initiation of parturition while both PG's and mainly PGF2alpha are in relation to the contractions and the duration of labor.