A pregnant women is advised by the gemara (Nidda 17a) to avoid stepping on cut human nails out of fear of miscarriage. What can she do if she has already stepped on them? Is there a way to "fix" things to avoid a miscarriage (chalilah)?
One source for the two approaches everyone is talking about is in the Ri MiLunel here (second column third paragraph). He writes that some say it is because of her fragility and some say it is because of sorcery. Interestingly, the way he formulates the second option - because of sorcery, not simply spiritual dangers - it would appear that he would hold that this does not apply in an era where we are generally not concerned about sorcerers. Couple that with the fact that (as others pointed out) according to the first option it doesn't seem logical that the danger should last longer than the moment she steps on the nails anyway, and we can basically conclude that according to the Ri MiLunel the answer to the question is she has nothing to worry about.
I believe there are 2 possible approaches. 1st the approach stated by Seth J that we wish to avoid the woman stepping on something and the shock and or disgust will cause her to worry and then subequently cause the loss of the unborn child G-d forbid! So in this case it would be appropriate to simply not worry and put faith in HKB'H.
If however the reason is something spiritual (e.g. the Zohar HaKodesh states that the first drop of semen goes to the nails) then there may well be a spiritual matter.
With all aspects - davening to HaShem can erase any tekana. The is a sefer by the Mevaser Tov (current Biala Rebbe) that writes even if the knife is beginning to cut ones throat davening to HaShem can tear up the decree.