As the vast majority of characters in Tanakh are Israelite, when new personalities are introduced, we tend to assume that they too are from the Children of Israel.1 Thus, in the case of the midwives, many readers take their Israelite ethnicity for granted. Moreover, there appears to be very good reason to do so, as "לַמְיַלְּדֹת הָעִבְרִיֹּת" translates literally as "to the Hebrew midwives," and these midwives are also described as being God-fearing.
However, there is room to wonder whether Paroh would turn to the Jews themselves to murder the Children of Israel's babies. Additionally, Paroh seems genuinely surprised that the midwives did not carry out his instructions. If they were Israelite, though, this would not have been so unexpected. This leads some exegetes to suggest a different reading of the phrase "לַמְיַלְּדֹת הָעִבְרִיֹּת" and to reconsider the identity of the midwives.