During the past few years enormous progress has been made in the under
standing of the molecular mechanisms involved in parturition; however,
the answer to the fundamental question of how labor is initiated rema
ins elusive. This is a very important question because alterations in
the timing of birth (preterm and post-term deliveries) are associated
with much of perinatal morbidity and mortality. Currently available tr
eatments for preterm labor are not clearly effective. Prevention of pr
eterm delivery by home uterine monitoring has been proposed; however,
the value of this technique has not been conclusively shown. A variety
of substances have been implicated in the genesis of labor, including
oxytocin, prostaglandins, cytokines, and endothelin. The role of infe
ction in preterm labor has also been extensively studied, but it seems
clear that a relatively small percentage of preterm labor is caused b
y infection. Attention has also focused on the role of estrogen and pr
ogesterone, and the possible uses of progesterone antagonists in the i
nduction of labor. A better understanding of the relationship of intra
uterine hypoxia and preterm delivery may also help us in establishing
treatment and prevention strategies.