Stages and Physiology of Lactation

Oxytocin: The Milk Ejection Reflex

While prolactin makes the milk, oxytocin is responsible for moving it out of the breast. When the nipple is stimulated by an infant's suckling, the hypothalamus prompts the posterior pituitary gland to release oxytocin. This hormone triggers the milk ejection reflex, also commonly known as the let-down reflex. This reflex causes the milk to be ejected from the alveoli into the ducts so the infant can consume it.

Exam Tip: Remember the distinction between the two hormones: Prolactin is for Production, and Oxytocin is for Output (ejection).

Evolution of Milk Composition

Human milk is a "living tissue" that changes its nutritional profile to match the infant's age and needs.

Colostrum

At birth, the mother produces colostrum, a clear, yellowish fluid. Colostrum is highly concentrated and serves as the infant's first "immunological vaccine". It is extremely rich in:

• Secretory immunoglobulin A (sIgA): The major immune globulin that provides broad-spectrum protection against bacterial, viral, and protozoal infections.
• Proteins, fat-soluble vitamins, and minerals.

Transitional and Mature Milk

As lactation progresses from colostrum to transitional milk and finally to mature milk, the nutritional density shifts:

• Decreasing components: Concentrations of immunoglobulins and proteins decrease.
• Increasing components: Levels of lactose, fat, and total calories increase to support rapid growth.

Effective Milk Removal: Positioning and Latch

For lactation to be successful, the infant must be able to effectively remove milk. Because milk is produced in response to feeding, the breasts never completely empty; however, frequent and effective removal is necessary to maintain supply.

Positioning

Proper positioning ensures the infant is comfortable and can access the breast easily. Recommended positions include:

• Skin-to-skin contact.
• Tummy-to-tummy orientation.
• Semi-reclined positions for the birther.

The Latch

The latch refers to how the infant takes the breast into their mouth. A correct latch involves the infant creating an adequate seal around the nipple, the areola, and the surrounding breast tissue. This seal is necessary to create the suction required for effective milk removal.

Clinical Note: The LATCH Assessment To evaluate breastfeeding success, clinicians often use the LATCH tool to assess:

• L: Latch (the seal between mouth and breast).
• A: Audible swallowing.
• T: Type of nipple (flat, inverted, or everted).
• C: Maternal comfort.
• H: Holding skills.

Monitoring Infant Intake

Because milk composition and volume change, clinicians must monitor the infant's output to ensure adequate intake.

Elimination Patterns

A reliable indicator of sufficient milk intake is the number of voids (urination) and stools.

Weight Management

It is normal for infants to experience a slight weight loss in the first few days of life. However, clinicians must monitor this closely to ensure it does not exceed safe limits.

To calculate the percentage of weight change, use the following formula: $\text{Percentage Change} = \frac{\text{Current Weight} - \text{Previous Weight}}{\text{Previous Weight}} \times 100$

Clinical Thresholds:

• A 5–7% weight loss over the first 3 days of life is considered normal.
• Infants should not lose more than 8% of their birth weight.
• By day 10–14, the infant should have returned to their birth weight.