Most women's waters break at the end of the first stage of labour, when the cervix (neck of the womb) is almost fully dilated. But for around 15% of pregnancies, breaking waters is the first sign of labour.
It can be a gush of up to a litre or just a trickle, so even if you're not sure, play safe and ring your midwife or the labour ward as you'll need to be examined.
Consultant obstetrician Dr Virginia Beckett, of the Royal College of Obstetricians and Gynaecologists, says, 'If your waters break early but you don't have any complications or problems, you'll normally be offered the option of waiting for 48 hours or inducing labour.
'We'd want labour to start within 48 hours to reduce any risk of infection, because once your waters break there's no barrier between your baby and the bacteria in your vagina.'
Lots of women choose to wait and will start contractions on their own in that time. However, if labour doesn't start spontaneously, you'll need to be induced.
Some hospitals induce labour by inserting gel or a pessary into the vagina which contains a hormone-like substance called prostaglandin. It helps ripen the cervix and stimulate contractions.
Alternatively, you might get offered a drug called Syntocinon through a drip in your arm to help kick-start your contractions.