This article is an excerpt from "The Nursing Mother's Problem Solver" by Claire Martin.
Q: My sister-in-law told me that if I supplement with formula, it will cause problems for my 6-month-old baby. I can't pump enough to give my day-care provider as much breast milk as she needs. Is it so bad to use formula to make up the difference?
A: If you're exclusively breastfeeding your baby, you usually don't need formula. But it can be difficult to pump enough to satisfy a growing baby, especially during growth spurts, if you're working too. Your baby can safely take both breast milk and formula. The only concern might be that if your baby is less than 6 weeks old, she could be susceptible to nipple confusion and find that bottle-feeding is easier than breastfeeding.
Look at it this way: At least your baby's had the advantage of a breast milk-only diet for 6 months. That's longer than many moms manage! And if you continue to nurse when you're with the baby, she'll still get the immunological and nutritional benefits of breast milk.