Spirulina is a blue-green algae that is sold as a supplement purported to have numerous health effects from boosting immune function to lowering cholesterol to helping prevent cancer. It is also sold as a general health booster that is high in protein, iron and other minerals.
There is not enough scientific information about consuming spirulina during pregnancy to make a determination on whether using it while pregnant or breast-feeding is safe.
The U.S. National Institutes of Health, for example, state on their website that not enough is known about the use of spirulina during pregnancy and breast-feeding, and therefore it is best to stay on the safe side and avoid use if you are pregnant or breast-feeding.
Finally, As far as accidentally eating something once while you're pregnant, there's really no reason to worry about it affecting your baby. It's extremely rare that one incident will cause serious problems. If you have concerns, just don't eat it again.
Dr Gupta, MD