Angels And Ordinary (non-prophet) Humans
Prophets were sent for specific Nations for preaching, under the guidance of Revelation and/or inspiration from Allah. A Special privilege and responsibility having far reaching consequences for the Prophets as well as for the Nation. These pious Female individuals were not Prophetesses in that sense. However they were the bearer/receiver of “Good News/Glad Tidings” from Angels. May be this has something to do with Tarbiyat(gromming). May be Allah talla wanted these ladies to pay special attention & care in raising and grooming these special children, whom were to be appointed Prophets latter on. However this is just Qiyas(assumption). Its also possible that all the Mothers of Prophets had received these glad tidings in one form or the other from Angels. However this is just a conjecture based on reports in the Quran about Mothers of Ismail, Ishaaq, Moosa, Maryam, Yahya & Essa(as) etc.. God knows best!
Please refer to the following response by Ghamidi Sahab in this regard: Discussion 4209 • Reply 4656