Study, 1987
What time of day does your period usually start?
Periods most commonly start at night or early in the morning. In about one-third of cases, bleeding had already begun by the time women woke up.
What they did
Researchers tracked 86 women across 4 to 6 menstrual cycles, noting the exact time menstruation began. For 48 women, they also recorded bedtime, wake time, when spotting started, and when period pain began.
What they found
70.4% of cycles started at night or within 4 hours of waking. In 29 out of 76 cycles, bleeding was already present on waking. Premenstrual spotting lasting more than 3 hours was reported by 67% of women. Menstrual cramps occurred in about 50% of women and typically happened around the time bleeding started. Only 13% of women had their period start within the same 3-hour window across four different cycles. Almost 50% had very different starting times from cycle to cycle.
What it means for you
Menstruation commonly starts at night rather than during the day. The timing varies significantly from cycle to cycle for most women. The main limit is this is a small observational study with no comparison group.
70.4%
cycles starting at night or within 4 hours of waking
67%
women with spotting lasting over 3 hours
86
women in the study
About the study
- Original title
- Analysis of the time of day of onset of menstruation
- Authors
- Donald JL, Fraser IS, Duncan L et al.
- Journal
- Clinical reproduction and fertility
- Year
- 1987
- Study design
- Study
- Participants
- 86
- Read the paper
- https://pubmed.ncbi.nlm.nih.gov/3690465/
Topics
Related studies
Randomised trial, 2025
Do vitamin D and E supplements reduce menstrual pain and PMS symptoms?
Systematic review, 2025
Does digital healthcare help manage period pain and PMS?
Cohort study, 2025
How common is PMS in Chinese teenage girls, and what factors are linked to it?
Systematic review, 2025
Does teaching adolescent girls about their menstrual cycle and health help reduce period pain and PMS?
Randomised trial, 2024
Does estetrol/drospirenone birth control improve PMS symptoms?
Cohort study, 2024
Is there a link between sleep and menstrual problems in teenage girls?