Progestins declined slowly in late gestation from about 15 ng/ml plasma until about 2 days prior to parturition, when levels decreased rapidly to about 3-4 ng/ml at delivery. A further decline in progestins was noted within 24 h after delivery with levels remaining low for up to 37 days postpartum. Progestin levels did not change during delivery. Corticosteroids, although variable in concentration, increased significantly 24 h prior to and during parturition. Estrogens increased continuously from 11 days prepartum (2 ng/ml) to 3 days prepartum (6.4 ng/ml), remaining constant through parturition with a precipitious decline observed by 24 h postpartum (2.5 ng/ml). Levels remained low (0.2 ng/ml) for up to 37 days after delivery.

In the 2 animals that aborted, progestin and corticosteroid patterns were somewhat similar to those noted for animals undergoing normal delivery, while estrogen levels differed from normal patterns in that estrogens declined in one animal and were low with a slight increase in the other animal prior to delivery. Although the number of observations is limited, it appears that premature delivery in the pig during late gestation due to disease processes is not accompanied by completely normal endocrine preparatory changes (estrogens in particular). This may be due to the fact that while the female may be able to respond in a normal manner to premature induction of labor, porcine fetuses appear to be immunologically incompetent (as compared to bovine and ovine fetuses) with fetal death the main result of exposure to stressor agents. Thus delivery may be preceded by fetal death which does not allow for the initiation of normal endocrine patterns.