24 hour rhythm in the timing of pre-labour spontaneous rupture of membranes at term

OBJECTIVE: To study the timing of pre-labour spontaneous rupture of membranes (SROM) in term pregnancies. DESIGN: Prospective cohort. SETTING: A maternity hospital in the United Kingdom. SAMPLE: Women who were more than 37 weeks gestation with confirmed spontaneous rupture of membranes and not in labour after 4 h. METHODS: Women who were admitted into labour ward with a diagnosis of spontaneous rupture of membranes after 37 weeks of gestation were included. The women's demographic details were recorded and inquiries about whether they had sexual intercourse in the preceding 12 h. The final outcome of their pregnancy was recorded and analysed. MAIN OUTCOME MEASURES: (1) The exact time of spontaneous rupture of membranes, (2) the time of onset of spontaneous labour, (3) delivery details. RESULTS: One hundred and ninety-six women were studied. A 24 h rhythm in the timing of spontaneous rupture of membranes was found with 33.2% occurring between 00:00 and 04:00 h. When contractions representing the onset of labour occurred there was no diurnal rhythm to the timing of onset of contractions. CONCLUSIONS: There is a 24 h rhythm in the timing of spontaneous rupture of membranes in term gestations. The physiological reasons for this rhythm are not understood at the present time.