While it's helped curb sudden infant death syndrome (SIDS) cases, the sleep-on-their-backs emphasis has scared parents away from tummy time at all, which is essential for infants to develop neck and back muscle strength, among other benefits.
According to the Slate article, "the less time infants spend on their stomachs, the slower they generally are to acquire motor skills during their first year, which means the potential delay of simple feats like lifting their heads as well as more complicated movements like rolling over, crawling and pulling to stand."
However, when a baby reaches these motor-skills milestones before he or she walks is proving crucial and can factor into long-term health and cognitive ability (delayed motor skills, lower IQs, even school-related problems), according to a growing number of studies cited by Slate.
The Slate writer goes on to note that doctors are not sounding any alarms on this trend because "children usually walk shortly after their first birthday regardless of how much tummy time they've had."
Not only is tummy time helpful in muscle development, it helps prevent flat head in babies. Babies usually begin to lift their heads when they're on their bellies at about 2 to 3 months old, making their way up to "baby push-ups" at about 4 to 6 months old. To help your baby get to these milestones, give him or her plenty of stretches of tummy time.
And remember, every baby reaches milestones at his or her own rate—there's no one-size-fits-all "normal" milestone chart.
Maria Vega is Fit Pregnancy magazine's copy editor.