With regard to what comes out of the pregnant woman before giving birth:
1. If it is blood and it comes out two or three days before the birth, accompanied by signs such as pain or cramps, then this is blood of nifaas; otherwise it is irregular bleeding which does not mean that she should stop fasting or praying.
It says in Kashshaaf al-Qinaa’ (1/219): If she sees blood three days or less before the child is born, accompanied by signs such as pain, then this is nifaas, like that which comes out at the time of birth. That which comes before the birth is not regarded as part of the period of nifaas. End quote.
2. If it is water like that which you have mentioned, then it comes under the same ruling as other vaginal secretions. It is taahir (pure) because it comes from the womb, and it invalidates wudoo', but it does not mean that she cannot pray or fast, because it is not regarded as nifaas.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked: Three days before giving birth some water came out of her accompanied by a little pain. Is that nifaas?
He replied: This is not nifaas, because nifaas is blood and not water. Moreover, if it was nifaas it would be accompanied by labour pains two or three days before giving birth. But if this occurs a long time before giving birth, then it is not nifaas, because nifaas is the blood that comes out at the time of birth or two or three days before it, accompanied by labour pains. As for water, that is not nifaas. End quote from Fataawa Noor ‘ala al-Darb.
For the ruling on secretions, see the answer to question no. 37752
And Allah knows best.