While the objective criteria are tremendously valuable, don't dismiss your subjective information. Listen to your own "mother's heart." There may be times when you feel an unshakable certainty that something is wrong even though you have been reassured that all is well. Once you have separated your feeling from normal worry and parental anxiety, give it credence and try diligently to search deeper for the cause of your concern.
If, on the other hand, your health providers, friends, or family are aware that you may have low milk produciton and are unsupportive or dubious of your breastfeeding efforts, convinced that successful breastfeeding is an impossibility, you may find that the subjective information your baby and your own heart provide is tremendously important in deciding for yourself whether breastfeeding is good for you and your baby. You may also find that objective resources will help you separate fact from fear in determining an accurate assessment of your baby's progress.
You must always put the nutrition and hydration needs of your baby before any emotional needs. Your baby must be fed no matter what. But remember that a baby can be fully supplemented with donated breastmilk or formula at the breast. As long as the baby is willing and able to, breastfeeding is always possible, and in almost all circumstances, the baby will receive some of your breastmilk. The true bottom line is that you must use all your resources, including those that are objective and subjective, to determine what is best for you and your baby.
References
Dewey, K., Nommsen-Rivers, L., Heinig, M., et al. Risk factors for suboptimal infant breastfeeding behavior, delayed onset of lactation, and excess neonatal weight loss. Pediatrics 2003 Sep; 112(3 Pt 1):607-19.
Dewey, K., et al. Growth of breast-fed infants deviates from current reference data: A pooled analysis of US, Canadian, and European data sets. Pediatrics 1995; 96(3):495-503.
Dewey, K., et al. Breastfed infants are leaner than formula-fed infants at one year of age: The DARLING study. Am J Clin Nutr 1993; 57:140-45.
Dewey, K., Heinig, M., Nommsen, L., et al. Growth of breast-fed and formula-fed infants from 0 to 18 months: the DARLING Study. Pediatrics 1992 Jun; 89(6 Pt 1):1035-41.
Dewey K., et al. Adequacy of energy intake among breastfed infants in the DARLING study: Relationships to growth velocity, morbidity, and activity levels. J Pediatr 1991; 119:538-47.
American Academy of Pediatrics, Policy Statement, Breastfeeding and the Use of Human Milk. Pediatrics 2005 Feb; 115(2):496-506.
Shrago, L. Adequacy of breastmilk intake: assessment and interventions. Presented at the La Leche League International Lactation Consultant Workshop. October 30, 1998, Chicago, IL.
Mohrbacher, N. and Stock, J. The Breastfeeding Answer Book, 3 rd Rev Ed. Schaumburg, IL: LLLI, 2003.
American Academy of Pediatrics, Policy Statement, Breastfeeding and the Use of Human Milk. Pediatrics 2005 Feb; 115(2):496-506.