Pregnancy / lactation

Topic Completed: 1 January 2015

Minor changes: 13 January 2021

Copyright: 2002-2021,, Inc.

PubMed Search: Breast [title] pregnancy and lactation [title]

Belinda Lategan, M.D.
Page views in 2020: 5,160
Page views in 2021 to date: 367
Cite this page: Lategan B. Pregnancy / lactation. website. Accessed January 24th, 2021.
Definition / general
  • Breast tissue becomes fully mature and functional once pregnant
  • Changes start at time of first missed menstrual period (2nd - 4th week) and are uneven throughout breast
  • Gross appearance
    • Increased pigmentation of nipple areolar complex, distension if superficial veins, Montgomery tubercles more pronounced
    • Enlargement of breast becomes apparent at month 5 of pregnancy
  • Microscopic features
    • As pregnancy progresses, changes become more pronounced
    • Size and number of lobules increase, epithelial cells enlarge, stroma becomes more vascular with small aggregates of inflammatory cells
    • Initial decrease in both inter and intralobular stroma with increase in adipose stroma as pregnancy progresses towards term
    • Epithelial cytoplasm becomes vacuolated, nuclei take on a hobnail appearance (resembles Arias-Stella reaction), secretions become evident
    • Myoepithelial cells become attenuated in lobules due to enlargement of cells but remain conspicuous in extralobular ducts (2nd and 3rd trimester)
  • Initially, placental HPL inhibits lactation but other hormones including estrogen, progesterone, TSH and ACTH maintain development of breast tissue
    • Initial secretions are high in protein, electrolytes and antibodies (especially IgA) → colostrum
  • Hormones of pregnancy also affect ectopic and accessory breast tissue, pre-existing benign fibroepithelial lesions and proliferative breast lesions
  • Commences ~ day 2 - 6 postpartum
  • Hormones from corpus luteum and placenta (progesterone, estrogen, HPL) initially suppress lactation during pregnancy
  • With delivery of placenta, HPL levels drop precipitously while prolactin levels remain high and initiate copious milk production (secretory activation)
    • Initial secretions are high in protein, electrolytes and antibodies (IgA especially) → colostrum
    • Secretory activation begins 30 - 40 hours postpartum
  • Crying or suckling stimulates hypothalamus to transport oxytocin to and release oxytocin from posterior pituitary → contraction of myoepithelial cells → expulsion of milk (milk ejection / letdown reflex)
  • Continued nursing or similar stimulation (i.e. manual / mechanical pumping) stimulates prolactin production to maintain lactation
  • Continued nursing or similar stimulation (i.e. manual / mechanical pumping) necessary to maintain lactation
  • Initial continued enlargement due to accumulation of milk
  • Prolactin levels drop, milk production decreases and then ceases, degenerated lobular epithelial cells are desquamated and phagocytosed by macrophages
  • Gradual return to prepregnancy state over 3 month period once nursing ceases
  • Lactational change may persist focally
    • "Residual lactating lobule" in women who have been gravid
    • Pseudolactational change (pseudolactational hyperplasia) - similar changes focally in breasts but in women who are not or have never been pregnant
  • Lobules remain enlarged compared to prepregnancy state
  • Lactational macromastia
    • Erythematous, edematous or painful breasts, with variable ulceration of overlying skin; usually recurs with subsequent pregnancies
  • Lactational change with psammoma body calcifications
    • Sporadic enlargement of lobules in nonpregnant women
    • Large, prominent psammoma bodies may present as suspicious clustered calcifications on mammography
  • Breast abscess
    • Lacation is most common period for breast infection
    • Cracks in nipple skin give entry to bacteria (Staphylococci, Streptococci)
    • Treated with antibiotics and expression of milk
  • Lacational adenoma
    • Palpable mass during pregnancy or lactation
    • Circumscribed mass of normal appearing breast tissue with lacational change
    • Size may change before and following a feeding
  • Galactocele
    • Tender mass due to rupture of ducts with leakage of milk into surrounding tissue
    • Induces chronic inflammatory response
    • Aspiration resembles milky fluid
  • Infarction
    • Arises in pre-existing benign lesions like fibroadenoma
    • Mitoses and necrosis may raise possibility of malignancy
  • Galactorrhea
    • Lacation in nonpregnant individual
      • No cause in up to 50% of individuals
      • Causes:
        • Prolactin secreting tumors (prolactinoma, pituitary adenoma)
        • Mechanical stimulation
        • Medication (methyldopa, opiates, SSRI, cimetidine, risperidone, other)
        • Primary hypothyroidism, renal failure
  • Malignancy

Images hosted on other servers:

Breast during lactation

Breast lobules during lactation

Microscopic (histologic) description
  • Acinar proliferation with minimal intra and interlobular connective tissue
  • Intralobular ducts form buds that become secretory alveoli with grape-like clusters and scant stroma
  • Epithelial cells accumulate cytoplasmic organelles to sustain postpartum lactation; glands have dilated lumina, contain lipid secretory vacuoles with large, apical nuclei resembling Arias-Stella reaction
  • May have clear cell change in ductal or lobular epithelium; these changes may also occur without pregnancy or hormonal manipulation (see pseudolactational hyperplasia)
  • Lactation:
    • Increase in number of lobules and number of acini within each lobule; reduction in interlobular and intralobular stroma; myoepithelial cells are present but difficult to identify
    • Luminal epithelial cells are secretory and have cytoplasmic vacuoles; after lactation ends, lobules involute over several months and are infiltrated by lymphocytes and plasma cells
    • Postlactational changes, present up to 5 years after cessation of lactation, include irregularly shaped lobules, angulated acini, flat epithelium, crenulated basement membrane and lymphocytes and plasma cells within intralobular stroma (Histopathology 1989;15:415)
Microscopic (histologic) images

AFIP images

8th month - ectatic acinar lumens lined by vacuolated epithelium with secretion, typical of late third trimester

Images hosted on other servers:

First trimester

Various images

Acinar proliferation

Involution of fibrofatty stroma


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