Last fall, the American Academy of Pediatrics astounded some parents and delighted others by declaring that newborns should sleep in the grown-ups' room for at least the first six months of life, and preferably for the first year.

That may not be the best advice, after all, according to a new study by Pennsylvania State University researchers.

Their work, published Monday in the journal Pediatrics, found that sharing a room with infants at ages 4 months and 9 months was associated with less sleep and poorer sleep quality for both baby and parents, as well as unsafe sleeping practices such as bed-sharing that the pediatrics group's recommendations sought to prevent.

The new findings come from Penn State's Intervention Nurses Start Infants Growing on Health Trajectories (INSIGHT) study of newborns and mothers. Part of an obesity prevention trial, the study's data were collected from 230 mother-baby pairs from January 2012 to March 2014.

Reinforcing previously issued safe sleep advice, the AAP last fall cautioned against bed-sharing by infants and parents as well as putting babies to bed with blankets or loose bedding, bumpers or stuffed toys. All those precautions, particularly avoiding sharing beds, have been associated with reducing the risk of infant death.

In the Penn State study, the mother-infant pairs were divided into three groups: "early independent sleepers," who slept without sharing a parent's room by 4 months of age; "later independent sleepers," who began sleeping in a separate room between 4 and 9 months; and those still sharing a room at 9 months.

Room-sharing at 4 and 9 months tended to coincide with less nighttime sleep than observed in the early independent sleepers.

"Perhaps our most troubling finding was that room-sharing was associated with overnight transitions to bed-sharing, which is strongly discouraged by the AAP," the Penn State study states.

Bed-sharing, the researchers found, was more common among the 4- and 9-month-olds who started the night in their parents' room but in their own beds. Room-sharers had four times the odds of being moved to a parent's bed during the night at both 4 and 9 months old. They also found nonindependent sleepers were more likely to be fed, either by breast or bottle, until they fell back to sleep.

"The fact is, when the AAP made their recommendation it was not based on data for 6- to 12-month-olds. It was expert opinion," said Ian M. Paul, Penn State pediatrics professor and chief of the Division of Academic General Pediatrics.

"We should be doing everything we can that has evidence to support it," said Paul, a pediatrician and parent. "We shouldn't be doing things that are not supported by evidence."

Rachel Y. Moon, professor of pediatrics at the University of Virginia School of Medicine, speaking for the AAP, said the fall recommendations gave parents more flexibility – 6 months to a year of room-sharing – and for now, they will remain.

However, Moon agreed that more study is needed.

She said existing studies have conflicted with each other on mothers' sleep experiences, and while room-sharing parents may be more sleep-deprived, "we don't know that for sure."