Some unexpected results in time distribution analysis of spontaneous deliveries

Objective: To study time distribution of spontaneous deliveries. Methods: A retrospective analysis of 1,791 spontaneous deliveries over a 4-year period (1993–1996) was made at the department of Obstetrics and Gynaecology, Civil Hospital, Fano, Italy. Circular statistics techniques (maximization of mean vector length) were used. Results: Some unexpected infradian disuniformities (with 60- and 90-hour periods) were observed. Moreover, a correlation between the distribution of spontaneous deliveries and the lunar phases was found. Conclusions: In this study, some unexpected infradian disuniformities were found. However, no biological explanations appear to be reasonable in light of current knowledge, so the interpretation of these results remains an open question.