Its a sakanah for a pregnant woman to step on cut nails. As per the Gemara, the sakanah is only when the nail is stepped on in its original place where it fell. If the nail falls to the ground and is then moved around it no longer presents a sakanah.
Generally with these kinds of sakanah, since we dont understand the reasons behind it, the prevailing opinion is that we dont extend the sakanah to anything more than what is said.