This is a very personal choice for many women, and can depend on personal preference. While some may prefer to wait until after the birth, others buy their nursing bras in advance. Each method can have pros and cons; it can often be tricky to choose a size too soon in advance when the breasts haven’t grown into their full size yet, and purchasing a nursing bra too late can be stressful. The majority of health experts recommend buying a nursing bra in the last month of pregnancy, as this is when you will have the best fit.