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Extracted from Survival Guide to Midwifery, 2nd Edition (2012) Diane M. Fraser and Margaret A. Cooper, Oxford; Churchill Livingstone: 2012. Courtesy Elsevier
Labour is the process of delivering the baby, the placenta, membranes and umbilical cord from the uterus via the vagina to the outside world. Regular uterine contractions together pressure from the descending, presenting part (the fetal head, or buttocks in a breach presentation) result in effacement and dilatation of the cervix to allow delivery of the baby.
Normal labour is spontaneous in onset between 37 and 42 weeks gestation. The process of labour is described as three stages.
Phases of the first stage of labour
The latent phase
Active first stage
The second phase of labour is the phase between full dilatation of the cervical os and the birth of the baby. Contractions become stronger and longer but may be less frequent. The membranes often rupture spontaneously (if they have not already done so). Fetal axis pressure increases flexion of the head, which results in smaller presenting diameters.
Contractions become expulsive as the fetus descends further into the vagina. Pressure from the presenting part stimulates nerve receptors in the pelvic floor and the woman experiences the urge to push. This reflex becomes increasingly compulsive and involuntary during each contraction. The mother's response is to employ her secondary powers of expulsion by contracting her abdominal muscles and diaphragm.
The fetal head becomes visible at the vulva, advancing with each contraction and receding between contractions until crowning takes place. The head is then born. The shoulders and body follow with the next contraction, accompanied by a gush of amniotic fluid and sometimes blood. The second stage culminates with the birth of the baby.
The time taken to complete the second stage of labour will vary considerably. Although some maternity units impose limits on its duration beyond which medical help should be called, these are not based on good evidence.
During the third stage of labour, separation of the placenta and membranes occurs as the result of an interplay of mechanical and haemostatic factors. The time taken for the placenta to separate from the uterine wall can vary, but any period up to 1 hour may be considered to be within normal limits. Once separation has occurred, the uterus contracts strongly forcing the placenta and membranes into the vagina, and contributing to haemostasis.
Uterotonic drugs such as ergometrine or oxytocin may be administered to stop the risk of bleeding or if it is deemed that there is a risk of excessive bleeding.
Royal College of Midwives (2012). Evidence Based Guidelines for Midwifery-Led Care in Labour. Latent phase. Available at: https://www.rcm.org.uk/sites/default/files/Latent%20Phase_1.pdf
Royal College of Midwives (2012). Evidence Based Guidelines for Midwifery-Led Care in Labour. Second stage of Labour. Available at: https://www.rcm.org.uk/sites/default/files/Second%20Stage%20of%20Labour.pdf
National Institute for Health and Care Excellence (2014). Intrapartum care for healthy women and babies (CG190). Available at: https://www.nice.org.uk/guidance/cg190