Extracted from Survival Guide to Midwifery, 2nd Edition (2012) Diane M. Fraser and Margaret A. Cooper, Oxford; Churchill Livingstone: 2012. Courtesy Elsevier
Rupture of the membranes
The optimum physiological time for the membranes to rupture spontaneously is at the end of the first stage of labour after the cervix becomes fully dilated and no longer supports the bag of forewaters.
The uterine contractions are also applying increasing force at this time.
Membranes may sometimes rupture days before labour begins or during the first stage.
If there are no other signs of labour but the history of ruptured membranes is convincing or obvious liquor is draining, then digital examination should be avoided owing to an increased risk of ascending infection.
If the diagnosis is not obvious, then one sterile speculum examination should be performed to try to visualise pooling of liquor in the posterior fornix; endocervical swabs may also be taken at this time.
The majority of women will labour spontaneously within 48 hours. After 48 hours an obstetrician may consider augmentation of labour.
Women with prelabour ruptured membranes should have their temperature recorded and be monitored for signs of fetal compromise associated with infection.
Occasionally, the membranes do not rupture, even in the second stage, and appear at the vulva as a bulging sac covering the fetal head as it is born; this is known as the 'caul'.
Sweeping or stripping of membrane
Sweeping the membranes can be an effective method of inducing labour in an uncomplicated pregnancy. During a vaginal examination, the clinician inserts a finger through the cervical os, and using a sweeping or circular movement, releases the fetal membranes from the lower uterine segment. The woman should be made aware that this procedure may cause some discomfort and bleeding.