Both Jeremiah and Jesaia are puzzling in that respect. The word used in both cases is "Beten" (stomach) not Womb (which is "Rehem"). At least, in the case of Jeremiah, he statement is (1:5) "before I created you, in stomach I knew you, and before you exited the womb, I dedicated you a Prophet to nations". Mind you, Jeremiah is not created yet when he is in the stomach or the womb, the Almighty, knowing the future, already knew him, but Jeremiah was not a being until he left the womb, god knew him before he "created him". (You'll find a similarity in Jesaia 49:5 "my creator from stomach to his slave set me to bring back Jakob to him...".
Both of these cases do not imply life prior to birth. Mind you, both of these prophets (particularly Jeremiah, since the Hebrew word "Yada " or to know (in the good old biblical sense between a man and a woman) is used in Jeremiah case, indicating a similarity in the circumstances of his birth to that of a later prophet Yeshua.
Zeev