DIURNAL RHYTHMS OF LABOR AND DELIVERY IN WOMEN - MODULATION BY PARITYAND SEASONS

OBJECTIVES: Our purpose was to evaluate in women the diurnal (24 hour) rhythms of the onset of labor and time of delivery and their modulati on by parity and seasons. STUDY DESIGN: A retrospective analysis was p erformed on 15,910 at term deliveries of single fetuses with noninduce d labor. RESULTS: A diurnal rhythm of labor onset, with peak frequency at 8 PM and 9 AM was observed in nulliparous women but not in multipa rous women. No diurnal rhythm of labor length was detectable. A diurna l rhythm of delivery, with peak values at 2 PM was evident in nullipar ous but not in multiparous women. In nulliparous women the two acropha ses of the diurnal rhythm of labor onset were closer in summer (10 hou rs) than in winter (13 hours). The acrophase of the diurnal rhythm of delivery progressively shifted to earlier hours from winter (5 PM) to summer (1 PM). CONCLUSIONS: These data show the attenuation of the diu rnal rhythms of labor and delivery in multiparous women and their modu lation by seasons.