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Plasma levels of 6-keto-PGF1 alpha and 13,14-dihydro-15-keto-PGF2 alpha (PGFM) were measured by high pressure liquid chromatography and radioimmunoassay during and up to 48 hours after term labor. PGFM levels increased during labor to reach values which at full dilatation, at delivery of the fetal head and at placental separation were each time higher than levels obtained earlier. In all women (n = 10) PGFM levels reached their maximum and started to decline within 10 min. after placental separation. Levels decreased to prelabor values within 2 to 3 hours after delivery and no temporary increases were observed within the first 2 days. Levels of 6-keto-PGF1 alpha on the other hand, showed no consistent trends throughout labor and the early puerperium. The observed changes are believed to be of relevance for ensuring adequate hemostasis after birth.

Urinary excretion of 6-keto-PGF1 alpha was measured by high pressure liquid chromatography and radioimmunoassay at various stages of pregnancy and labor. In the first trimester of pregnancy, urinary 6-keto-PGF1 alpha concentrations were not different from those measured before pregnancy, but they showed a significant increase in the second trimester of pregnancy (p less than 0.001). The levels rose further in the third trimester, although this increase was not statistically significant when compared to levels obtained in the second trimester. There was no evidence for a significant change in 6-keto-PGF1 alpha excretion with the onset of labor. During well-established, progressive labor mean values of 6-keto-PGF1 alpha excretion were about twice as high as before the onset of labor, but the range of values during labor was so wide that there was no statistical difference with values obtained in the second half of pregnancy. It is concluded that the increase in the urinary excretion of 6-keto-PGF1 alpha occurs later in pregnancy than the increase in TXB2 excretion and that labor at term is not associated with marked changes in 6-keto-PGF1 alpha excretion.

Urinary TXB2 excretion was measured during pregnancy and labor using high pressure liquid chromatography and radioimmunoassay. From the first trimester onwards TXB2 levels in urine of pregnant women (n = 60) were significantly (p less than 0.001) higher than in non-pregnant women (n = 12) and they increased, albeit not significantly, with advancing gestation. Labor was associated with a two-fold increase in urinary TXB2 excretion. Levels in established labor were significantly higher than at any other time in pregnancy (p less than 0.001), but the levels in incipient labor showed considerable overlap with these in late pregnancy. Thus urinary TXB2, while not necessarily originating from the pregnant uterus, appears to reflect the uterine activity of labor and may be the expression of a general stimulation of prostanoid production during parturition.