Menstrual Flow

Menstrual flow in Apple Health records a description of bleeding, together with an interval and a marker for the start of a cycle. It can describe a whole period in one sample or changes across several samples. A row count alone cannot tell you how many periods were recorded.

These labels do not measure blood volume or specify a product-change frequency. The code for none is 5, so numeric averages and comparisons such as “higher code means heavier bleeding” would be misleading. The older menstrual-flow enum is deprecated in favor of HKCategoryValueVaginalBleeding from iOS 18 and watchOS 11; the type identifier and these raw values remain applicable.

The required HKMetadataKeyMenstrualCycleStart Boolean marks the first sample of a recorded cycle. For a single interval covering the period it is true; later samples describing that period use false.

Calculate gaps between verified start markers rather than every pair of flow records. First inspect missing markers, duplicated starts, overlapping sources and intervals covering several days. A gap across an unlogged cycle is not evidence that the physiological cycle lasted that long. The interval length can describe logged bleeding duration; it does not independently validate it.

Cadence follows logging choices, with no continuous sensor stream. A source may save one interval for a period while another saves daily intensities. Separate per-day coverage, interval duration and start-to-start gaps so changes in logging format are not mistaken for a change in bleeding.

Cervical mucus, ovulation tests and temperature can be aligned to recorded cycle starts when enough observations exist. Use source-aware dates and retain unknown days.

No menstrual-flow rows were present in the research window. There were no observed flow proportions, cycle-start markers or between-cycle intervals to graph. Missing rows do not mean no bleeding or no periods.

A flow category cannot identify a cause of bleeding, establish fertility or substitute for clinical assessment. Logging an explicit none differs from leaving a date blank. Apple says Cycle Tracking should not be used as birth control. Preserve changes to dates and source provenance when reviewing a revised period history.