# Situation: A 22-year-old primipara gave birth vaginally to a healthy term newborn at a lying-in clinic, and her episiotomy was repaired. She plans to breastfeed exclusively, and the nurse follows her through the first days after birth. The mother asks when her breasts will start making larger amounts of milk. The nurse's answer is based on the usual timing of lactogenesis II. When does this usually occur?

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> subject: Nursing Practice II — Maternal and Child Health Nursing

## 문제

Situation: A 22-year-old primipara gave birth vaginally to a healthy term newborn at a lying-in clinic, and her episiotomy was repaired. She plans to breastfeed exclusively, and the nurse follows her through the first days after birth.

The mother asks when her breasts will start making larger amounts of milk. The nurse's answer is based on the usual timing of lactogenesis II. When does this usually occur?

## 보기

1. Within the first 24 hours after birth
2. Between days 7 and 10 after birth
3. Between days 2 and 5 after birth **✔ 정답**
4. At about 2 weeks after birth

**정답: 3**

## 해설

In the first days the breasts secrete colostrum, which is small in volume but rich in antibodies and protein. The milk "comes in" (lactogenesis II) around days 2 to 5, often with fullness or engorgement. Transitional milk then gives way to mature milk at about 2 weeks.

## 심화 해설

Timing of Lactogenesis II

Lactogenesis is divided into two phases. Lactogenesis I begins during pregnancy and results in the production of colostrum, a thick, yellowish fluid that is low in volume but concentrated with immunoglobulins, protein, and fat-soluble vitamins. After delivery of the placenta, the abrupt fall in progesterone allows prolactin to drive the transition to lactogenesis II, the onset of copious milk secretion. This is the phase mothers recognize as the milk "coming in," often accompanied by breast fullness, warmth, and sometimes engorgement.

Lactogenesis II typically occurs between 2 and 5 days postpartum. The earliest measurable changes are biochemical: milk lactose, citrate, and glucose concentrations rise sharply as tight junctions in the mammary epithelium close and copious secretion begins [3]. Clinically, the mother perceives fullness or "coming in" around the same window, although the subjective sensation may lag slightly behind the biochemical shift [3].

Milk volume data support this timeline. In a longitudinal study of exclusively breastfeeding women, milk transfer to the infant was low on days 1 and 2 and increased rapidly to 498 ± 129 g/day by day 5, followed by a slower rise to 753 ± 89 g/day during months 3–5 [1]. This steep early increase corresponds to the lactogenesis II window and confirms that the transition is well underway by the middle of the first week.

| Phase | Timing | Secretion | Clinical features |
| --- | --- | --- | --- |
| Lactogenesis I | Pregnancy through first 1–2 days postpartum | Colostrum | Small volume; high immunoglobulin and protein content |
| Lactogenesis II | Days 2–5 postpartum | Copious milk secretion begins; transitional milk | Breast fullness, warmth, possible engorgement |
| Mature milk | About 2 weeks postpartum | Mature milk | Stable composition; volume continues to rise gradually |

Key point! The onset of lactogenesis II is defined biochemically and clinically by the shift from low-volume colostrum to copious milk secretion, not by the attainment of full mature milk volume. Mature milk composition is reached later, around 2 weeks, which is why option 4 is incorrect for the "milk coming in" question.

Watch out! Delayed onset of lactogenesis II is defined as onset at ≥72 hours postpartum . Risk factors include higher body mass index, older maternal age, larger infant birth weight, and metabolic conditions such as diabetes . For a primipara, delayed onset is more common than in multiparas, so nurses should assess for signs of successful transition—audible swallowing, relaxed feeding, and the mother's report of breast fullness—during the first several days.

The nurse can explain to this mother that her breasts are already producing colostrum in the first day or two, and that the larger volume of milk usually arrives between days 2 and 5. Frequent, effective breastfeeding or milk removal during this window supports the hormonal and local control mechanisms that complete lactogenesis II.References (research sources)

- [1]Studies in human lactation: milk volumes in lactating women during the onset of lactation and full lactation.Research articleNeville MC, Keller R, Seacat J, Lutes V, Neifert M, Casey C (1988) · DOI: 10.1093/ajcn/48.6.1375

- [3]Milk lactose, citrate, and glucose as markers of lactogenesis in normal and diabetic women.Research articleArthur PG, Smith M, Hartmann PE (1989) · DOI: 10.1097/00005176-198911000-00016

## 임상 시나리오

Timing of Lactogenesis IIClinical Guide for Postpartum Breastfeeding Support
The onset of copious milk secretion, or lactogenesis II, typically occurs between 2 and 5 days postpartum. This is the phase mothers recognize as the milk "coming in."

The trigger is the abrupt fall in progesterone after placental delivery, which allows prolactin to drive milk synthesis. Before this, the breasts secrete colostrum, which is low in volume but rich in antibodies.

CautionMothers may experience engorgement during this window. Educate on frequent feeding and proper latch to prevent complications such as mastitis.

## 핵심 개념

- **Lactogenesis II** — The onset of copious milk secretion following delivery, triggered by a drop in progesterone, typically occurring 2-5 days postpartum.
- **Colostrum** — The first milk produced, small in volume but rich in immunoglobulins and protein, secreted during late pregnancy and the first days after birth.
- **Engorgement** — Breast fullness, warmth, and swelling that can occur when milk 'comes in' and milk volume increases rapidly.
- **Prolactin** — The hormone responsible for driving milk synthesis and secretion, which becomes more active after the placenta is delivered.

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