What is the expected normal rate of cervical dilatation in the active phase?

In the active phase, the cervix is traditionally expected to dilate at at least ~1 cm/hour (the basis of the alert line), with descent of the presenting part.

The minimum acceptable rate is often quoted as ~1 cm/hour for primigravidae and slightly faster for multigravidae; newer evidence shows active-phase progress can be slower (especially 4-6 cm) and still be normal, so rigid cut-offs are applied cautiously.

Clinical relevance. Knowing the expected dilatation rate (and that early active-phase progress can be slower) avoids over-diagnosing failure to progress.

More Detail

Normal rate of cervical dilatation

The expected rate of dilatation underlies the partogram's alert line.

Traditional expectation

• In the active phase, the cervix is expected to dilate at at least ~1 cm/hour - the basis of the alert line.
• Accompanied by descent of the presenting part.
• The minimum acceptable maximum-dilatation rate is often quoted around 1 cm/hour (primigravidae), slightly faster in multigravidae.

Updated evidence

• Contemporary data show that active-phase progress can be slower than 1 cm/hour - particularly between 4 and 6 cm - and still be normal.
• So rigid time-based cut-offs are applied cautiously, considering the whole clinical picture (fetal and maternal wellbeing) rather than diagnosing 'failure to progress' too early.

Use

• The partogram (alert/action lines) flags slow progress for closer assessment, not automatic intervention.