When a pregnant woman feels contractions, should she stop praying, and does she have to makeup the missed prayers?
Question

                When does a woman in labour (for childbirth) stop performing the salah? Does she still perform the salah if she is having contractions but no fluid has come from her body yet?
Praise be to Allah.We put the following question to Shaykh
    Muhammad ibn Saalih al-‘Uthaymeen, may Allaah preserve him:
If a woman whose pregnancy has reached full term passes blood
    and has pains, but she does not know whether these are the contractions that will lead to
    childbirth or contractions that will later ease off [“practice” contractions,
    also known as Braxton-Hicks contractions], should she pray or not?
He answered, may Allaah preserve him:
Of course, there are two things we may assume here: 
The first is that the pregnancy will continue without
    contractions.
The second is that the apparent case is that these are
    contractions, so she should stop praying.
If this is what usually happens to her, and she may carry on
    having contractions for four or five days without giving birth, then in this case she
    should still pray.
Question:
If she acts upon the second assumption, then the contractions
    ease off, should we tell her to make up the prayers she has missed?
Answer:
It is preferable to make them up, because she took her
    decision on the basis of an assumption.
In summary, then:
If this woman usually has contractions for a number of days
    – more than two or three – then this is not nifaas and she should pray. If that
    is not what usually happens, then we assume that it is nifaas in the sense that she should
    stop praying. If she stops praying, then it turns out that it was not nifaas, then in this
    case we say that if she makes up the prayers she has missed, this is good, and if she does
    not make them up, there is nothing wrong with that because she acted on an assumption.
And Allâh knows best.