Adam Clarke on Exodus 1:15

Hebrew midwives - Shiphrah and Puah, who are here mentioned, were probably certain chiefs, under whom all the rest acted, and by whom they were instructed in the obstetric art. Aben Ezra supposes there could not have been fewer than five hundred midwives among the Hebrew women at this time, but that very few were requisite see proved on Exo 1:19 (note).