When does lactation (milk production) begin during and after pregnancy, and what are early signs?

1. Early prep work: breasts start making colostrum mid‑pregnancy

Medical and patient‑education sites consistently report that the breasts begin producing the first milk—colostrum—around the middle of pregnancy, commonly cited as roughly weeks 16–22 (GetBoober, Jackson Health, Medela, Cleveland Clinic) ^{[1] [2] [3] [4]}. That early production is hormonally driven: pregnancy estrogen and progesterone promote duct and gland development while prolactin starts increasing, priming the mammary tissue well before delivery ^{[4] [3]}.

2. Visible signs during pregnancy: what people commonly notice

Signs you may observe before birth include breast fullness, increased vascularity (visible veins), nipple and areola changes, tenderness, and occasional leakage of thick, yellow colostrum—especially later in pregnancy—though many pregnant people have no obvious leak and that doesn’t predict postpartum supply ^{[3] [1] [8]}. Patient guides emphasize that leaking or not leaking during pregnancy “has no bearing on” breastfeeding ability ^{[9] [8]}.

3. The big switch after birth: when milk “comes in”

The dramatic increase in milk volume—lactogenesis stage II—typically follows delivery and the placenta’s expulsion, which alters hormone levels; most parents experience this between 2 and 5 days postpartum, though timing varies and delayed onset can occur ^{[1] [5] [6]}. Lactation experts note that mature milk production ramps up over days to weeks and supply often stabilizes by about four weeks, with the first two weeks seeing the biggest changes ^{[3] [7]}.

4. Signs that milk is increasing in the days after birth

Common postpartum signals include heavier, fuller breasts or mild engorgement, a change in milk color/texture (from sticky colostrum to thinner transitional milk), more frequent and effective baby feeds, and the baby waking or feeding more often—these are described as practical markers that supply is establishing ^{[10] [7] [11]}.

5. When timing is different: delays and contributing factors

Health authorities and lactation resources warn that factors such as complicated delivery, heavy blood loss, certain medications, preterm birth, thyroid issues, or other medical problems can delay the expected 3–5 day onset and extend it to 7–14 days or more; when milk is delayed, early lactation support is advised ^{[6] [12] [13]}. Sources stress seeking a lactation consultant early if there are concerns ^{[3] [6]}.

6. Variation is normal: why some people don’t notice early signs

Multiple sources emphasize that many people never notice colostrum leakage during pregnancy and that lack of visible signs does not equal inability to breastfeed—lactation is hormonally prepared and then demand‑driven after birth ^{[9] [11] [4]}. Conversely, seeing colostrum in pregnancy simply indicates the process has started, not the exact postpartum quantity.

7. Practical takeaways and when to get help

If you notice colostrum leakage, tenderness, or breast changes, those are normal pregnancy signals of preparation ^{[1] [8]}. If after birth your milk hasn’t increased by day 3–5, or if baby isn’t gaining or feeding well, sources advise contacting a lactation consultant or healthcare provider to assess latch, feeding frequency, and any medical contributors to delayed lactation ^{[5] [3] [6]}.

Limitations and disagreements in the record

Sources agree on the broad outline—colostrum mid‑pregnancy, milk increase a few days postpartum—but differ slightly on exact week ranges (some say 16–20, others 16–22) and on phrasing about when the body is “fully capable” (end of second trimester vs. “midway” producing colostrum) ^{[1] [2] [14] [4]}. Available sources do not mention specific prevalence numbers for who will notice leaks during pregnancy or precise percentages for delayed lactation, so population‑level rates are not cited here (not found in current reporting).