Reference for Niddah 108:18

בפושרין מעת לעת

only the doubt of having given birth to a male child, and is there no doubt as to the possibility of the birth of a female child?<span class="x" onmousemove="('comment',' Of course there is. The birth of the latter is as possible as the birth of the former and the possibility, therefore, exists that the woman is unclean for fourteen days. ');">¹⁶</span>

Jastrow