Yes, pregnancy can cause lumps in your breast, and the vast majority are benign. The hormonal surge that prepares your body for breastfeeding dramatically reshapes breast tissue, and that process can produce distinct, palpable lumps that weren’t there before. Still, any new lump during pregnancy deserves evaluation, because roughly 19 out of every 100,000 pregnancies involve a breast cancer diagnosis.
Why Pregnancy Changes Your Breast Tissue
Your breasts undergo a near-complete architectural overhaul during pregnancy. In the first trimester, rising estrogen drives the milk ducts to branch and extend, gradually replacing fat tissue with denser glandular tissue. Blood flow to the breasts increases significantly. By the second and third trimesters, progesterone takes the lead, expanding the milk-producing lobules while the surrounding fat and fibrous tissue shrinks to make room.
Prolactin, the hormone responsible for milk production, adds another layer of change. It stimulates the milk-producing cells to mature and fill with tiny fat droplets. Small amounts of milk can actually be secreted as early as week 16. All of this proliferation increases breast density and can create areas of thickened, lumpy tissue that feel noticeably different from your pre-pregnancy breasts. In many cases, what feels like a “lump” is simply a region of glandular tissue growing faster or more densely than the surrounding area.
Most Common Types of Pregnancy-Related Lumps
Galactoceles (Milk-Filled Cysts)
Galactoceles are the most frequently identified benign breast mass during pregnancy and breastfeeding. They form when a milk duct gets blocked, trapping milk in a cyst. They typically appear in the third trimester or after breastfeeding stops, though they can show up during active nursing too. A galactocele usually feels moderately firm and painless, sitting close to the nipple area, and most measure 1 to 2 cm. A hallmark feature is that they fluctuate in size throughout the day, sometimes shrinking noticeably right after a feeding. Unless they become infected, they don’t cause redness, fever, or significant pain.
Fibroadenomas
Fibroadenomas are solid, rubbery lumps made of glandular and connective tissue. Many women already have small ones without knowing it. During pregnancy, the high concentrations of estrogen, progesterone, and prolactin can cause existing fibroadenomas to grow substantially, sometimes rapidly enough to become noticeable for the first time. In rare cases, they can reach several centimeters. New fibroadenomas can also develop during pregnancy for the same hormonal reasons.
Lactating Adenomas
These are benign tumors unique to pregnancy and breastfeeding. They arise directly from the milk-producing tissue as it proliferates. They typically feel like a well-defined, movable lump and are among the most common solid breast masses found during pregnancy.
Mastitis and Abscesses
Mastitis is a breast infection that can create a painful, swollen area that feels like a lump. It’s most common in the first six weeks of breastfeeding but can occur during late pregnancy as well. The affected area is typically red, warm, and tender. You may also have a fever, nausea, or purulent discharge from the nipple. If untreated, mastitis can progress to a breast abscess, a walled-off pocket of pus that feels like a firm, fluctuant mass. Abscesses sometimes require drainage.
How Lumps Are Evaluated During Pregnancy
Ultrasound is the standard first-line imaging tool for evaluating a breast lump during pregnancy. It uses sound waves rather than radiation, and there are no documented adverse effects on the fetus. The American College of Obstetricians and Gynecologists identifies ultrasound and MRI as the imaging techniques of choice for pregnant patients.
If the ultrasound shows anything suspicious, a core needle biopsy is safe to perform at any point during pregnancy. The procedure has a very low complication rate, though there is a small risk of infection, bruising, or, rarely, the development of a milk fistula. Because pregnancy makes breast tissue denser and harder to read on imaging, clinical guidelines recommend biopsy for any lesion that looks uncertain rather than waiting until after delivery. Mammography, while involving low-dose radiation, is not withheld when clinically needed. The radiation exposure falls well below the threshold associated with fetal harm.
When a Lump Could Be Something Serious
Pregnancy-associated breast cancer is uncommon, occurring in roughly 19 out of every 100,000 pregnancies globally. That rate is slightly lower in the Americas, at about 14 per 100,000. However, the incidence has been slowly rising over recent decades, and it accounts for 10% to 20% of all breast cancers diagnosed in women under 30.
Certain features make a lump more concerning. Watch for skin dimpling or puckering over the lump, a lump that feels fixed in place rather than movable, thickening or swelling of part of the breast, redness or flaky skin on the nipple or breast, nipple retraction (pulling inward), bloody or non-milk nipple discharge, or a change in the overall size or shape of one breast. None of these signs automatically means cancer, but each one warrants prompt evaluation. The challenge during pregnancy is that normal breast changes, like increased size, tenderness, and darkening of the nipple, can mask or mimic warning signs, which is why any distinct new lump should be checked rather than assumed normal.
What Happens After Delivery
Many pregnancy-related breast lumps resolve on their own. Galactoceles often shrink once breastfeeding stops and the milk ducts are no longer active. Lactating adenomas typically regress as hormone levels return to their pre-pregnancy baseline. Fibroadenomas that enlarged during pregnancy may partially shrink but don’t always return to their original size.
Based on clinical experience documented in case reports, lactation-related changes in breast tissue generally resolve within about six months after breastfeeding ends. If a lump persists beyond that window, or if it changes in character during follow-up, further evaluation with imaging or biopsy is typically recommended. Lumps that were biopsied during pregnancy and confirmed benign still benefit from a follow-up check after this six-month period to make sure they’ve behaved as expected.