There are many physical signs, and emotional reactions, that can happen for the woman throughout the 1st stage of her labour. Some signs can be very typical of certain phases, others can happen during any of the phases. The following are descriptions of the more common signs that you may notice, and some interpretations of why they may occur.
The waters can break (known as 'membranes rupturing'), at any time during the birth process, even just as the baby is being born. If the waters break during the early phase of 1st stage, and you are at home, you would need to follow the same procedure as for prelabour. In brief, this would be to check the colour of the amniotic fluid (if possible). If it is clear, or pink, this is normal, any green or brownish discolouration could possibly indicate meconium staining. Contact your hospital or caregiver for advice. To revise this information you may wish to read waters breaking, no contractions.
If the waters haven't broken before this, then they are more likely to break towards the end of the 1st stage of labour (this will happen for about 75% of women). The waters tend to break when the cervix becomes fully open (or 10cm dilated), and the baby starts to move down the birth canal. These changes usually put pressure on the bag of waters to burst. If there is enough leeway in the bag or sac, the membrane may move down to the opening of the woman's vagina, to bulge out like a giant bubble between the woman's legs. (Often prompting the woman, and her partner, to clarify with their caregiver "What is that?")