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Updated: Aug 11, 2026

Time-lapse Microscopy of Early Embryogenesis in Caenorhabditis elegans
Published on: August 25, 2011
A time to be born
M Anderka1, E R Declercq, W Smith
1Office of Statistics and Evaluation, Bureau of Family and Community Health, Massachusetts Department of Public Health, Boston 02108-4619, USA. marlene.anderka@state.ma.us
Objectives:
This study used a large, population-based data set (n = 619,455) to establish reference standards of the timing of spontaneous vaginal births.
Methods:
Low-risk births in Massachusetts from 1989 to 1995 were studied. This group comprised 242,276 births that met the following criteria: singleton, vertex, vaginal births with a birthweight of between 2500 and 4000 g; gestation between 37 and 42 weeks; a 5-minute Apgar score greater than 6, and no induction or stimulation.
Results:
Low-risk births displayed a mild circadian pattern, with a peak between 11:00 AM and 1:00 PM and a trough between 11:00 PM and 1:00 AM. Subgroup analysis showed no clear differences except for parity.
Conclusions:
Reference standards should be developed and used as comparative norms for hospital and practice-based perinatal studies of diurnal patterns of birthing.
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