Spontaneous rupture of membranes refers to the breaking of the membranes of the placenta that form the sac of fluid around baby, allowing amniotic fluid to leak out the vagina. This results in gushes or trickles of fluid. In approximately 10% of pregnancies at term, the waters will break prior to any contractions.
Once the waters are broken there is an increased chance of commencing regular contractions and an increasing risk of infection in the fluid around baby. By 12 hours after rupture of membranes approximately 50% of women will be contracting. By 24 hours approximately 75% of women will be contracting but the other 25% may take days to come into labour. The risk of infection increases after rupture of membranes with infection being more likely after 24 hours. Infection in the amniotic fluid can make baby very unwell and is potentially life-threatening.
In the 1990's a large study of women with ruptured membranes at term were randomised to either being induced immediately with intravenous Syntocinon or vaginal prostaglandin or waiting up to 4 days before being induced with intravenous Syntocinon or prostaglandin. Those who were not immediately induced were sent home with oral antibiotics and a thermometer to monitor their temperature. Most returned prior to the 4 days either in labour or with concerns or having become impatient for something to happen. There was no statistical difference in the outcomes. There was no statistical increase in life threatening infection in the group that waited while taking their oral antibiotics. There was no statistical increase in Caesarean sections in those who were induced immediately. When the women were surveyed after birth, the group that was happiest with their care were the ones who were immediately induced with Syntocinon. They had been taken to Delivery Suite and immediately had one-on-one care from the diagnosis of ruptured membranes until baby was born. The group that were least happy with their care were the ones that were sent away to await events.
As this study was not conclusive about the optimum management for ruptured membranes at term, women who present with ruptured membranes at term are given a choice. One option is for immediate augmentation with intravenous Syntocinon so that the contractions will commence or be enhanced. Another option is to wait for a short time and at the next most convenient time, usually the following morning so that labour occurs during the day, Syntocinon can be commenced if contractions have not started. After regular contractions start, there may still be many hours of labour (e.g. 8 to 10 hours for first labour) and the risk of infection continues to rise during this time.
If there is meconium stained liquor, this may mean that baby has passed meconium due to some stress eg cord entanglement. It is safest for baby to be delivered. This may be achieved by continuous fetal heart monitoring by CTG and immediate induction of labour with Syntocinon. If there are signs of fetal distress on the CTG, a Caesarean section may be needed or if fetal distress occurs in the pushing stage then help with vacuum or forceps may be required to deliver baby.
If a woman is known to be a Group B Streptococcus (GBS) carrier (i.e. GBS has been cultured from vaginal swab or urine this pregnancy), then immediate antibiotics and Syntocinon induction with continuous monitoring is the safest. GBS is a bacterial organism that commonly colonises the skin of the vagina and peri-anal area. It is this organism which is most likely to cause infection after rupture of membranes. Fortunately, this organism is usually sensitive to Penicillin and other antibiotics are available for those that have a Penicillin allergy.
When a woman presents with ruptured membranes, a vaginal swab can be collected but the culture takes three days to complete so this swab is not useful for decision making. For most women, GBS status is not known. Even if previous vaginal swabs have not detected GBS, it is still possible for this bacteria to be the cause of infection after ruptured membranes.
If baby is not delivered or likely to be delivered by 18 hours of ruptured membranes, intravenous antibiotics are commenced to help protect baby from infection. It takes two hours for the levels of antibiotics to reach protective levels in the baby and it is preferable for antibiotics to be given four hours before delivery.
Administration of antibiotics may be avoided if labour occurs, or is induced, and delivery occurs before antibiotics are required. After 24 hours of ruptured membranes, even with antibiotics that target GBS, other organisms may cause infections that are resistant to these antibiotics.
If at any stage there are signs of severe infection with maternal fever and fetal baseline tachycardia, it may be the safest option to deliver baby by Caesarean section, if vaginal delivery is not imminent, so baby can be treated directly with antibiotics. It is the risk of life- threatening infection in term infants that compels us to encourage labour rather than waiting too long for spontaneous labour.