Leaking colostrum during pregnancy

By trimester

Weeks 1–13

1st trimester

Colostrum production is already quietly starting at the cellular level as early as 12 to 16 weeks, right around the end of the first trimester, even though you won't see or feel any of it yet.

Weeks 14–27

2nd trimester

Some people begin noticing a little leaking in the second trimester, though it's just as normal not to. Breast changes are already underway either way as your body prepares for feeding.

Weeks 28–birth

3rd trimester

This is when leaking colostrum is most commonly noticed, if it happens at all. A supportive nursing pad can help if it's frequent enough to be bothersome, and it isn't a sign that anything needs to happen sooner than planned.

What does the evidence show for leaking colostrum?

• Colostrum production begins early, with alveolar cells in the breast starting to secrete it between 12 and 16 weeks of pregnancy in a process called lactogenesis I, though it usually isn't noticeable until it can be expressed from the breast by the third trimester. 1
• Colostrum is compositionally different from the milk that comes in later: it has higher protein and immune-antibody content and less carbohydrate and fat than mature breast milk, including secretory IgA that helps protect a newborn from infection. 1
• High progesterone from the placenta keeps milk production limited to small amounts throughout pregnancy, and it's only after delivery, when progesterone drops and prolactin, cortisol, and insulin rise, that full milk production takes over. 2
• Prolactin is already elevated during pregnancy, but the receptors that let it act on breast tissue are suppressed by high progesterone, which is part of why colostrum stays limited before birth even though the hormone that drives full milk production is already present. 3
• Signs of a breast infection, including redness, warmth, swelling, pain, and sometimes fever or nipple discharge, are different from the ordinary clear-to-yellow leaking that can happen before birth and are worth mentioning to your provider. 4

When should I call my provider about leaking colostrum?

A pink or blood-tinged tinge in leaking colostrum can be normal, especially early on, but discharge that's foul-smelling, or breast changes like redness, warmth, swelling, or fever, point toward an infection rather than ordinary prenatal leaking and are worth a call to your provider. Leaking that starts very early, well before the third trimester, or comes with breast pain out of proportion to normal tenderness, is also worth mentioning at your next visit. None of this is common, but it's specific enough to flag when it happens. Whatever the pattern, any symptom that feels beyond your usual range is a reason to call: obstetric teams expect these questions and would rather hear early than late.