ruby necklace

Question

hi rabbi, There is a popular segulah mentioned in Rabbeinu Bachya(scuz' the pronunciation) for a pregnant woman to wear a ruby necklace. Assuming that we are doing the things that we are supposed to: 1) does the Rav hold that this is a good idea? 2) may it be worn on shabbos? 3) if yes, may it be worn attached around an undergarment, or only as a necklace(around the neck)? thank you and have a good shaabos! martin