Reference for Yevamot 83:26

אלא משום דחסה אי הכי דידיה נמי דידיה חייס עילויה הכא נמי חייס עילויה

is a preventive measure against the possibility of turning the foetus into a sandal.<span class="x" onmousemove="('comment',' [H] 'a flat fish', hence an abortion that has the shape of a flat fish, assumed to be caused by intercourse during pregnancy. ');">⁴²</span> If so, [this should apply in the case] of one's own wife also!<span class="x" onmousemove="('comment',' During pregnancy. V. supra n. 7. ');">⁴³</span>

Jastrow