It is normal for the breasts to enlarge during pregnancy.
Normal histology of the breast during lactation.
Mammoplasia is the normal or spontaneous enlargement of human breasts.[1] Mammoplasia occurs normally during puberty and pregnancy in women, as well as during certain periods of the menstrual cycle.[2][3][4] When it occurs in males, it is called gynecomastia and is considered to be pathological.[4] When it occurs in females and is extremely excessive, it is called macromastia (also known as gigantomastia or breast hypertrophy) and is similarly considered to be pathological.[5][6][7] Mammoplasia may be due to breast engorgement, which is temporary enlargement of the breasts caused by the production and storage of breast milk in association with lactation and/or galactorrhea (excessive or inappropriate production of milk).[8]Mastodynia (breast tenderness/pain) frequently co-occurs with mammoplasia.[9][10]
A 1997 study found an association between the SSRIs and mammoplasia in 23 (39%) of its 59 female participants.[26] Studies have also found associations between SSRIs and galactorrhea.[24][28][29][30] These side effects seem to be due to hyperprolactinemia (elevated prolactin levels) induced by these drugs, an effect that appears to be caused by serotonin-mediated inhibition of tuberoinfundibulardopaminergicneurons that inhibit prolactin secretion.[26][28][29] The mammoplasia these drugs can cause has been found to be highly correlated with concomitant weight gain (in the 1997 study, 83% of those who experienced weight gain also experienced mammoplasia, while only 30% of those who did not experience weight gain experienced mammoplasia).[26] The mammoplasia associated with SSRIs is reported to be reversible with drug discontinuation.[30] SSRIs have notably been associated with a modestly increased risk of breast cancer.[31] This is in accordance with higher prolactin levels being associated with increased breast cancer risk.[32][33]
^Arnold G. Coran; Anthony Caldamone; N. Scott Adzick; Thomas M. Krummel; Jean-Martin Laberge; Robert Shamberger (25 January 2012). Pediatric Surgery. Elsevier Health Sciences. pp. 773–. ISBN978-0-323-09161-9.
^Ruth A. Lawrence; Robert M. Lawrence (26 October 2015). Breastfeeding: A Guide for the Medical Profession. Elsevier Health Sciences. p. 60. ISBN978-0-323-35776-0. The cyclic changes of the adult mammary gland can be associated with the menstrual cycle and the hormonal changes that control that cycle. Estrogens stimulate parenchymal proliferation, with formulation of epithelial sprouts. This hyperplasia continues into the secretory phase of the cycle. Anatomically, when the corpus luteum provides increased amounts of estrogen and progesterone, there is lobular edema, thickening of the epithelial basal membrane, and secretory material in the alveolar lumen. Lymphoid and plasma cells infiltrate the stroma. Clinically, mammary blood flow increases in this luteal phase. This increased flow is experienced by women as fullness, heaviness, and turgescence. The breast may become nodular because of interlobular edema and ductular-acinar growth.
^Milligan D, Drife JO, Short RV (1975). "Changes in breast volume during normal menstrual cycle and after oral contraceptives". Br Med J. 4 (5995): 494–6. doi:10.1136/bmj.4.5995.494. PMC1675650. PMID1192144. [M]any women report breast changes during the normal menstrual cycle, with a feeling of fullness and a tingling sensation immediately before menstruation.1 Women taking oral contraceptives also seem to experience similar breast symptoms.2 It has been claimed that there are also pronounced changes in breast volume during the normal menstrual cycle, with maximum values occurring in the week before menstruation.3
^Dancey, Anne; Khan, M.; Dawson, J.; Peart, F. (2008). "Gigantomastia – a classification and review of the literature". Journal of Plastic, Reconstructive & Aesthetic Surgery. 61 (5): 493–502. doi:10.1016/j.bjps.2007.10.041. ISSN1748-6815. PMID18054304.