Four weeks is often when breastfeeding mothers begin to think about pumping and storing extra breastmilk. (verywellfamily.com)
Do you have extra breastmilk which has not expired yet but you know you will not use it? (themilkmeg.com)
Often babies will lose 10 or more percent of their birth weight initially and may require supplementation to gain it back via extra breastmilk or formula. (health-foundations.com)