Mothers who breastfed their newborns did not appear to get less sleep than new moms who used formula or a combination of the breast milk and formula, researchers found.
A study of 80 new mothers found that neither objectively measured sleep nor the moms' perception of sleep quality differed based on feeding practices through the first 12 weeks of a baby's life, Hawley Montgomery-Downs, PhD, of West Virginia University in Morgantown, and colleagues reported online ahead of the December issue of Pediatrics.
These findings should ease the concerns of mothers who have heard that breastfed babies sleep less and wake up more often in the middle of the night, the researchers commented.
"Efforts to encourage women to breastfeed, as currently endorsed enthusiastically by the American Academy of Pediatrics, should include information about sleep," they wrote.
"Specifically, women should be told that a choice to formula feed does not necessarily equate with improved sleep," Montgomery-Downs and co-authors continued. "The risks of not breastfeeding should be weighed against the cumulative lack of evidence showing any benefit of formula feeding on maternal sleep."
To explore the common notion that women who breastfeed get less sleep, Montgomery-Downs and her colleagues recruited expectant women through childbirth classes, community ads, and word of mouth. A total of 80 new mothers were found eligible for the study and the team collected sleep data from the women through the first 12 weeks postpartum.
The researchers conducted their analysis in two-week increments, with the new moms divided into three groups -- those who exclusively breastfed, those who bottle fed only, and those who combined the two infant feeding methods.
The mothers wore a wrist actigraphy unit to objectively measure total sleep time, sleep efficiency, and sleep fragmentation, with data collected by a personal digital assistant (PDA). Subjective measures of sleep were also recorded in the PDA.
Of the objective sleep measures, there was only one significant between-group difference, which occurred on week 10 -- mothers who used a combination of breastfeeding and bottle feeding had better sleep efficiency compared with those who used formula feeding alone (P=0.021).
However, mothers who breastfed exclusively did not have impaired sleep for any measure compared with the other women.
For the subjective measures of nocturnal awakenings, total nocturnal wake time, and sleep quality, there were no significant differences based on feeding method, although breastfeeding mothers tended to have more nocturnal wake time than those using formula.
Similarly, there were no differences between the groups on any measure of daytime sleepiness or fatigue.
Because of the negative result of the study, the researchers conducted a post hoc analysis of the study's statistical power and concluded that "if a moderate to large effect existed, we would have found it within our sample."
They suggested that, even if breastfeeding mothers are waking up more often to feed their babies, then the act of breastfeeding itself may compensate by allowing mothers to return to sleep more quickly -- perhaps because of the reduced exposure to ambient light and physical activity compared with those mothers who need to prepare formula.
Montgomery-Downs and her colleagues noted that the findings may not be generalizable to mothers with a history of depression or anxiety, because such women were excluded from the study cohort.
"This is important," the authors wrote, "because women who are depressed are less likely to continue breastfeeding."
Additionally, they wrote, the study may have been biased because women who could not be contacted for the study were younger, had less education, had lower incomes, and were less likely to breastfeed.
The study was funded by a grant from the NIH.
The authors reported that they had no conflicts of interest.