The average hospital scored 63 out of 100, the Centers for Disease Control and Prevention reported Thursday.
"There is a lot of room for improvement," said Deborah Dee, a CDC epidemiologist who co-authored the report.
About a quarter of hospitals reported giving formula or some other supplement to more than half of their healthy, full-term newborns. The practice was common even when mothers were able and willing to breast-feed, Dee said.
Of hospitals who gave supplements, 30 percent gave sugar water and 15 percent gave water.
Experts say there are no good nutritional reasons to use those, but it is commonly done to quiet crying babies separated from their mother. Sometimes it's done to test a baby's ability to feed - even though such a test is usually not necessary, Dee said.
Breast-feeding is considered beneficial to both mothers and their babies. Breast milk contains antibodies that can protect newborns from infections, and studies have found breast-fed babies are less likely to become overweight that those fed with formula.
But breast-feeding can be frustrating for new mothers because of nipple pain or the misperception that they're not producing enough milk. It's crucial that moms get proper breast-feeding advice and encouragement those first few days after birth, said Dr. Sheela Geraghty, a lactation expert at Cincinnati Children's Hospital Medical Center.
"It's wonderful that hospitals and birth centers are being examined because if moms aren't helped right there, where are they going to be helped?" Geraghty said.
The research was based on questionnaires filled out last year by about 2,700 U.S. maternity hospitals and birth centers. Hospitals were scored on supportive efforts, like offering breast-feeding tips and keeping the mother and the infant together. They also were evaluated on practices detrimental to breast-feeding, including supplemental feedings or including infant formula samples in gift packs for mothers.
Hospitals may regard the gift packs as benign, but the practice interferes with breast-feeding, said Laurence Grummer-Strawn, chief of the CDC's nutrition branch.
"They don't understand they're implicitly endorsing a product and they're giving an easy out for when parents are tired" to use the formula, he said.
States in New England and on the West Coast scored highest, and the South did the worst. Vermont and New Hampshire topped the list, tied with a score of 81. Arkansas had the poorest score, 48.
The highest score for a hospital or birth center was 98; the lowest was 12. The CDC did not release individual scores.