The first few days after a baby’s birth involve rapid nutritional changes. Colostrum, often called “liquid gold,” is the initial milk produced, highly concentrated with nutrients, protective antibodies, and growth factors matched to a newborn’s needs. Though small in volume, this thick, yellowish substance acts as a protective shield, lining the baby’s gut and boosting their immature immune system. By Day 4, the body enters the transitional phase, where the first signs of increasing milk supply become apparent. Understanding these biological shifts is important to ensure the baby is feeding adequately.
The Transitional Phase: Colostrum to Mature Milk
The transition from colostrum to mature milk is a predictable biological shift that typically begins between Day 2 and Day 5 after birth. This period is when the mother’s body initiates copious milk production, often described as the milk “coming in.” The sudden increase in volume is triggered by a hormonal cascade following the delivery of the placenta.
The rapid drop in the pregnancy hormone progesterone, combined with sustained high levels of the milk-making hormone prolactin, signals the body to move into the full lactation phase. This process causes many to notice their breasts becoming noticeably firmer, fuller, and sometimes tender. The milk produced during this time is called transitional milk, which is a blend of colostrum and emerging mature milk components.
As the volume increases, the milk’s appearance shifts from the thick, deep yellow of colostrum to a thinner, whiter, or bluish-white color. This change indicates that the volume of fluid and fat content is rising, marking the progression toward mature milk. While the hormonal trigger occurs regardless of feeding frequency, sustained production is driven by milk removal, following the principle of supply and demand.
Expected Feeding Volume on Day 4
Day 4 marks a significant increase in the baby’s intake volume compared to the first 48 hours of life. A newborn’s stomach capacity grows rapidly, and by Day 4, it can hold approximately 22 to 27 milliliters (about 0.75 to 1 ounce) per feeding.
The average amount of milk consumed per feeding on Day 4 is estimated to be between 30 and 60 milliliters (1 to 2 ounces). This range requires the baby to feed frequently because the stomach capacity is still small. Over a 24-hour period, the total volume of milk consumed is substantially higher than during the first two days.
Newborns typically feed often, averaging 8 to 12 times in a 24-hour period. Feeding on demand, or whenever the baby shows hunger cues, is the most effective way to ensure the baby meets their nutritional needs and to further stimulate the increasing milk supply. The frequent removal of milk from the breast during this transitional phase helps establish a robust long-term milk supply.
Indicators the Baby is Eating Enough
Since parents cannot directly measure the volume of milk transferred during a nursing session, observing the baby’s output and behavior is the most reliable way to monitor adequate consumption. By Day 4, a healthy newborn should produce at least four wet diapers in a 24-hour period. The urine should be pale yellow, indicating sufficient hydration.
In terms of bowel movements, a baby on Day 4 should be passing at least three to four soiled diapers. The color of the stool should be visibly transitioning from the dark, tarry meconium of the first days to a greenish-brown or even starting to become the mustard-yellow, seedy stool characteristic of a milk-fed baby.
During the feed itself, signs of effective milk transfer include hearing or seeing the baby swallow regularly after the initial rapid sucking. The baby should appear calm and satisfied after most feeds, and the parent’s breast should feel softer, indicating that milk has been removed. Monitoring weight gain is also important, as steady gain after the initial, expected weight loss confirms adequate intake.