These small glands are thought to be protective of the areola and help keep it healthy during pregnancy and lactation. You should simply rinse the breasts with clear water and avoid soaps and oils which can irritate the great tissue, this is particularly true in breastfeeding. This is one of the many changes you may notice in the breasts during pregnancy and one that will be helpful at maintaining elasticity in breastfeeding.
Many women worry about these or try to pop them. This is not necessary and can be painful or cause infection if you try to pop them. Simply leave them alone. If you are concerned about them, ask your doctor or midwife for more information.
Doucet, Sébastien; Soussignan, Robert; Sagot, Paul; Schaal, Benoist (2009). "The Secretion of Areolar (Montgomery's) Glands from Lactating Women Elicits Selective, Unconditional Responses in Neonates". In Hausberger, Martine. PLoS ONE 4 (10): e7579. doi:10.1371/journal.pone.0007579. PMC 2761488. PMID 19851461.