Stages of Labour

The first stage of labour is divided into 3 phases.

Phase 1- latent stage with cervical effacement < 3cm dilation of the cervix and some descent of the head. This phase can be up to 10-12 hours in a nulliparous woman, the contractions may or may not be painful but most healthy women have this stage at home. Phase 2 - acceleratory phase from 3 cm dilation during which time uterine activity increases and the head descends. The cervix continues to dilate about 1cm/hour in a nulliparous woman but quicker for multiparous. Phase 3 - transition phase. Increasing activity and the onset of the expulsion of the head of the baby.

The second stage of labour is from full dilatation until birth of the baby.  There may be a passive second stage in which further descent is awaited (especially if an epidural is used), followed by the active second stage where maternal effort (eg by Valsalva manoeuvre) is used to push the baby out through the pelvic outlet. The baby is said to be “crowning” as the head distends the vulva and perineum and the ‘crown’ of the head is easily visible.

The third stage is from birth of the baby until delivery of the placenta. The uterine muscles contract to stop blood loss once the placenta has separated and the placenta delivers within 60 minutes-usually quicker. This 3^rd stage can happen by itself or can be actively managed by giving oxytocin, clamping the cord and using controlled cord traction to deliver the placenta. This reduces blood loss but on the other hand the medications used can cause nausea and vomiting and hypertension.

Here is another diagram from your book giving a pictorial representation of cervical effacement and dilation.