In this study the investigators will compare the effects of vaginal progesterone, intramuscular applied progesterone and topical progesterone on uterine electromyographic activity (EMG)in patients in preterm labor. Electrodes will be placed on the abdominal surface of pregnant patients in preterm labor and the EMG activity recorded for 30 minutes before and following treatments for up to 48 hours. In addition data on delivery times will be recorded when patients delivery vaginally or by Cesarian section. Eligibility criteria: Healthy patients without infection or rupture of membranes with gestational ages between 24 to 34 weeks. Outcome measures: Comparisons of uterine EMG activity (EMG amplitude, frequency, and specific information on EMG bursts) from measurements before treatment to following treatments with progesterone preparations at various times (at 2,4,8, 12,24 and to 48 hours following treatment) and delivery times of patients on various treatments (hours or days following treatments, average delivery times in patients treated by various formulations). Comparisons of mean values in uterine EMG activity (EMG amplitude, burst frequency and frequency of signals in a burst, power spectrum analysis of the bursts and peak power density spectrum of bursts) from before treatment to following treatments at 2 to 24 hours will be compared. Also the time of delivery following treatments will be obtained and the average time of delivery following the various treatments compared.
