INTERPRETING MOTOR MILESTONES: WHAT PERCENTILE DO THEY REPRESENT?

Most websites and infographics offer little advice on interpreting the gross motor milestones. From 2004 until March 2022, the CDC milestones described what 50% of infants and children did at a given age. Essentially, the CDC was trying to describe what the “average” child did. In early 2022, the CDC presented a new, more evidencebased list of milestones. There was an uproar among many parents and health professionals, because it appeared that the standards had been lowered. But, this was not the case. Instead, the new list of developmental milestones describes what 75%, or 3/4, of children can do at a given age. In statistical conventions the top 75% usually represents a typical pattern.

This change was done to encourage earlier referral. The thinking was, that if a milestone reflects the 50th percentile, pediatricians recognized that 25% of typically developing infants, or children, did not achieve that milestone, at a particular age. The Academy of Pediatrics and the CDC understood that this thought process resulted in a "wait and see approach."

By changing the list of milestones to represent the 75th percentile, pediatricians will be less likely to delay referral for formal assessment and intervention. While there remains some controversy over the changes, it is helpful to understand the thought process behind revising them.

Several changed gross motor milestones confused parents and upset therapists. For instance, the time frame for walking went from 15 months to 18 months. The CDC was not lowering the standard. The standard is essentially the same. 50% of toddlers are walking at 15 months but 75%, or more, are walking at 18 months.

If parents are concerned that a delay is not being picked up, there are precursors of

walking, like "Walks holding on to furniture." (12 months), or "Takes a few steps on his own" (15 months). "Takes a few steps on his own" and "walks without holding on" both describe walking. By distinguishing these phases and describing them specifically, the CDC adds clarification. This should guide caregivers more effectively.

MOVING AHEAD: When it come to skills like running, jumping, and throwing, cultural and contextual factors can determine the rate of achievement.

WINDOWS OF DEVELOPMENT

The World Health Organization (WHO) has proposed another way of looking at gross motor milestones. Their research studied typically developing, well-nourished children from 6 countries: Brazil, Ghana, India, Norway, Oman and the USA. They found that the sequence of development was consistent across cultures, except 4.3% of the babies never crawled. The WHO looked at what 99% of infants do. Their study revealed that milestone achievement can occur over wide ranges, which they call "Windows of Achievement."

Some infants sat independently at 3.8 months while some achieved sitting at 9.2 months. For unsupported walking, the range was even wider: from 8.2 months to 17.8 months. The study demonstrates how variable motor development can be, even for children without challenges.

CULTURAL, ENVIRONMENTAL, AND CHILD-REARING PRACTICES MAY IMPACT MOTOR DEVELOPMENT

Most gross motor screening and assessment tests available to practitioners have been developed in the US or Canada. The tests are based on research done in Western, Educated, Industrialized, Rich, and Democratic (known as WEIRD) countries. In these countries, there is some homogeneity in child rearing practices and culture.

Cross-cultural studies show that child rearing practices, as well as cultural beliefs, may influence early child development. Some practices accelerate development of motor skills. In cultures like Kenya and Cameroon, 5-month-olds are frequently put in unsupported sitting postures. These infants tend to achieve independent sitting earlier than those from cultures like the US, where this practice is not considered safe. Some cultures like Jamaica or the Au hunter-gatherers of Papua New Guinea, frown on putting babies on the ground for either practical, hygiene, or religious reasons. Crawling has many benefits but these infants develop typically though they do not crawl.

KEY CONCEPTS : GROSS MOTOR MILESTONES

Remember: No need to hesitate or delay, seeking advice is the better way.