A mother may choose to breast-feed her infant while maintaining an otherwise active life. This may continue for weeks or months, depending on the mother's preference.
Is it safe to scuba dive while breast-feeding?
From the standpoint of the child, the mother's breast milk is not unduly affected. The nitrogen absorbed into the body tissues is a component of breathing compressed air or other gas mixes containing nitrogen. This form of nitrogen is an inert gas and plays no role in body metabolism. Although nitrogen accumulates in all of the tissues and fluids of the body, washout after a dive occurs quickly. Insignificant amounts of this nitrogen would be present in the mother's breast milk; there is, however, no risk of the infant accumulating this nitrogen.
From the mother's standpoint, there is no reason for a woman who is breast-feeding her child to avoid diving, provided there is no infection or inflammation of the breast.
Just for the record; I breastfed both my babies until they were nearly 2 years old, and often waiting on the beach with the babysitter for my return as they were hungry. Aside from a salty boob, my babies had no complaints. I now have healthy boys age 6 and 3.