The Gemorah (Moed Katan 18a; Niddah 17a) tells us that “the righteous burn their nails, the pious bury them, and the wicked carelessly discard them.”
The Gemorah explains that nail clippings must be carefully disposed of lest a pregnant woman pass over them and miscarry.
See Mishnah Berurah in OC 260:1:6 or 260:6, Mogen Avraham beginning of Siman 260, Be’er Heitev 260:2, Rivevos Ephtraim Vol. 8 Siman 88:1, Likutei MaHarich Seder hanhagos Erev Shabbos Dibur hamaschil V’Ayin B’Rama.
Based on the above it would be prudent for a pregnant woman to avoid a nail salon.