Relationship of circadian rhythms of uterine activity with term and preterm delivery

Objective: Our aim was to document the presence or significance of circadian uterine activity rhythms in pregnant women who delivered at term and preterm. Study Design: We measured uterine activity in 19 women divided into a control group (low risk for preterm labor, term delivery, n = 7), a group at high risk for preterm labor, term delivery (n = 6), and a group at high risk for preterm labor, preterm delivery (n = 6). Patients were hospitalized for 24 hours every 2 weeks from 26 weeks' gestation until delivery. Uterine activity was measured continuously by external tocodynamometer. Results: Patients delivering at term demonstrated a nocturnal surge (4 to 7 AM) in uterine activity the last 80 days before delivery (n < 0.05, analysis of variance). Patients delivered preterm showed an initial nocturnal surge of uterine activity similar to those delivered at term, but this disappeared 24 days before delivery (n>0.05, analysis of variance). Conclusion: Uterine activity nocturnal surges normally precede term delivery. These surges are lost in women who deliver prematurely.