Final answer:
A pediatrician may recommend supplementing with formula for a nursing child after the mother becomes pregnant with another child to ensure adequate nutrition.
Step-by-step explanation:
During pregnancy, the lactating mother's body goes through changes to prepare for lactation and breastfeeding. When the baby suckles at the breast, prolactin is released, stimulating the mammary glands to produce milk. However, as the pregnancy progresses and a new baby is expected, there might not be enough breast milk supply to meet the needs of both children. In such cases, a pediatrician may recommend supplementing with formula to ensure that the nursing child receives adequate nutrition.