The limitations of these studies are that they have small numbers as well as a higher than expected preterm delivery rate among placebo patients. Because of the previous controversy as to the effectiveness of progesterone noted in the 70's - 80's it is incumbent upon other centers to carry out new investigational trials in an effort to confirm their results. Secondly, the studies were limited to singleton pregnancies who were "at risk" for preterm delivery thus not surveying three groups with the highest preterm delivery rate: 1.) Multifetal gestations and cervical insufficiency; 2.) Those who have preterm labor in the current pregnancy that have been tocolyzed; 3.) Women with preterm premature rupture of the membranes.