Some nursing moms argue that wearing a sports bra reduced their milk flow while others say that it did not have any effect on them. Sports bras do not have an underwire but they tend to be a bit tight since they are designed to hold your breasts during exercise. They have a band that puts a lot of pressure on your chest and may cause the milk ducts to clog. Luckily, some companies like Motherhood Maternity have introduced sports bras that are appropriate for nursing moms as they do not put a lot of pressure on you. I believe it is okay to wear these maternity sports bras rather than the normal ones made for sports only.