A simple test is described at a link provided below. It is not always easy to tell by looking. The simplest first step in assisting the nipples to stand out is to wear breast shells designed to put gentle pressure on the area around the nipples. If you find that the shells are not making a difference, or have severely inverted nipples, You might want to try either the Nipplette, sold through Avent UK, or the Evert-It Nipple Enhancer. See links to both below.
Nature provides many changes in the breasts during pregnancy.
Besides the changes of the structures inside the breast, there are changes in the nipples and areolas. These enlarge somewhat and the tissue become more elastic, and . There are some things that adoptive moms can do to simulate these effects. Tactile stimulation of the nipple and areola is essential in getting the message to the brain that there is a baby nursing who needs milk. However, since the invention of the bra, many women in industrialized countries have developed a nipple sensitivity that it more extreme than nature intended it to be.