Rupture of the membrane sac surrounding the fetus that is not closely followed by labour or that occurs before labour is due
The fetus is protected in the uterus inside a fluid-filled bag called the amniotic sac. The membranes that form this sac normally rupture during or just before the start of labour, but in about 1 in 14 women they rupture early.
It is not known exactly what causes the membranes to break early, although in some pregnancies, premature rupture of the membranes may be due to an infection that spreads upwards to the uterus from the vagina.
Rupture of the membranes causes the amniotic fluid to leak from the vagina. The amount of fluid lost varies from a light trickle to a heavy gush. If your membranes break at night, you may wake in a pool of liquid, which can easily be mistaken for urine. If you think that your membranes may have broken, you should contact your doctor or midwife.
If labour does not commence within a few hours of the membranes rupturing, there is a risk of the uterus or the fetus becoming infected. There is also a possibility of a cord prolapse, in which the umbilical cord drops into the cervix or vagina. If this occurs, the blood supply to the fetus may be reduced, depriving it of oxygen (see Fetal distress). In women who have not yet reached week 37 of pregnancy, rupture of the membranes may lead to premature labour. In this event, the risk to the fetus of an early delivery must be balanced against the risk of an infection developing if labour is stopped.
You may need to be admitted to hospital and monitored for evidence of an infection. Your doctor will feel your abdomen and examine you internally using a speculum to hold the vagina open. He or she will also take your temperature because a fever may indicate an infection. Your doctor may also take a vaginal swab and arrange for blood tests to look for signs of an infection. If there is an infection, you will be treated with antibiotics. The heart rate of the fetus may be monitored (see Fetal monitoring) to look for indications of fetal distress. If you are at least 37 weeks into your pregnancy, labour usually begins within 24 hours of rupture of the membranes. Labour will usually be induced (see Induction of labour) if it fails to start.
If you are 36 weeks pregnant or the fetus is mature enough for delivery, labour may be induced; otherwise, you may be kept in hospital and monitored for signs of infection. If you are less than 34 weeks pregnant, you may be given injections of corticosteroids to help the fetus’s lungs mature.
After birth, the baby may need to be monitored in a special care baby unit, but most babies are healthy and have no ill effects from early delivery.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.